@article{strathprints88432,
month = {March},
title = {Crystal-field analysis of photoluminescence from orthorhombic Eu centers and energy transfer from host to Eu in GaN co-doped with Mg and Eu},
year = {2024},
journal = {Journal of Luminescence},
url = {https://strathprints.strath.ac.uk/88432/},
issn = {0022-2313},
abstract = {Gallium nitride co-doped with magnesium and europium shows great potential for active layers in red light emitting diode structures due to strong and sharp luminescence emission around 620 nm. In this work, sharp and intense Eu3+ luminescence lines from the excited states of the 5DJ (J=0, 1) multiplets to the ground states of the 7FJ (J=0, 1, 2) multiplets have been analyzed using a C2v crystal-field equivalent operator Hamiltonian. A model of Eu centers with the C2v symmetry has been proposed to be an Eu3+ complex accompanied by either a pair of nitrogen and gallium vacancies (VN-VGa) or a pair consisting of a nitrogen vacancy and magnesium impurity (VN-MgGa) in the vicinity of the Eu ion based on the crystal-field analysis, the selection rules and the observed polarization of the Eu3+ luminescence lines. Energy transfer from the host to the Eu ions under band-to-band excitation occurs through electron-hole recombination between VN with the electron-like state and VGa or MgGawith the hole-like state; these may be associated with the shallow-trapped or deep-trapped states, respectively, proposed as the energy transfer mechanism in previous literature.},
author = {Yamaga, Mitsuo and Singh, Akhilesh K. and Cameron, Douglas and Edwards, Paul R. and Lorenz, Katharina and Kappers, Menno J. and Bo{\'c}kowski, Michal}
}

@Article{strathprints84031,
author = {Cameron, Douglas and Coulon, Pierre-Marie and Fairclough, Simon and Kusch, Gunnar and Edwards, Paul R. and Susilo, Norman and Wernicke, Tim and Kneissl, Michael and Oliver, Rachel A. and Shields, Philip A. and Martin, Robert W.},
journal = {Nano Letters},
title = {Core-shell nanorods as ultraviolet light emitting diodes},
year = {2023},
issn = {1530-6992},
month = {February},
number = {4},
pages = {1451--1458},
volume = {23},
abstract = {Existing barriers to efficient deep UV LEDs may be reduced or overcome by moving away from conventional planar growth and towards three dimensional nanostructuring. Nanorods have the potential for enhanced doping, reduced dislocation densities, improved light extraction efficiency and quantum wells free from the quantum confined Stark effect. Here, we demonstrate a hybrid top-down/bottom-up approach to creating highly uniform AlGaN core-shell nanorods on sapphire repeatable on wafer scales. Our GaN-free design avoids self-absorption of the quantum well emission, while preserving electrical functionality. The effective junctions formed by doping of both the n-type cores and p-type caps were studied using nanoprobing experiments where we find low turn on voltages, strongly rectifying behaviours and significant electron beam induced currents. Timeresolved cathodoluminescence measurements find short carrier liftetimes consistent with reduced polarisation fields. Our results show nanostructuring to be a promising route to deep-UV emitting LEDs, achievable using commercially compatible methods.},
doi = {10.1021/acs.nanolett.2c04826},
keywords = {nanorods, LEDs, UV LED, nanowire, core-shell, AIGaN, semiconductors, electron microscopy, Optics. Light, Atomic and Molecular Physics, and Optics},
url = {https://doi.org/10.1021/acs.nanolett.2c04826},
}

@Article{strathprints78914,
author = {Kusch, Gunnar and Comish, Ella J. and Loeto, Kagiso and Hammersley, Simon and Kappers, Menno J. and Dawson, Phil and Oliver, Rachel A. and Massabuau, Fabien C.-P.},
journal = {Nanoscale},
title = {Carrier dynamics at trench defects in {InGaN/GaN} quantum wells revealed by time-resolved cathodoluminescence},
year = {2021},
issn = {2040-3372},
month = {December},
pages = {402--409},
volume = {14},
abstract = {Time-resolved cathodoluminescence offers new possibilities for the study of semiconductor nanostructures - including defects. The versatile combination of time, spatial, and spectral resolution of the technique can provide new insights into the physics of carrier recombination at the nanoscale. Here, we used power-dependent cathodoluminescence and temperature-dependent time-resolved cathodoluminescence to study the carrier dynamics at trench defects in InGaN quantum wells - a defect commonly found in III-Nitride structures. The measurements show that the emission properties of trench defects closely relate to the depth of the related basal plane stacking fault within the quantum well stack. The study of the variation of carrier decay time with detection energy across the emission spectrum provides strong evidence supporting the hypothesis that strain relaxation of the quantum wells enclosed within the trench promotes efficient radiative recombination even in the presence of an increased indium content. This result shines light on previously reported peculiar emission properties of the defect, and illustrates the use of cathodoluminescence as a powerful adaptable tool for the study of defects in semiconductors.},
doi = {10.1039/D1NR06088K},
keywords = {cathodoluminescence, semiconductor nanostructures, quantum wells, Physics, Materials Science(all)},
url = {https://doi.org/10.1039/D1NR06088K},
}

@Article{strathprints79454,
author = {O'Hanlon, T. J. and Zhu, T. and Massabuau, F. C.-P. and Oliver, R. A.},
journal = {Ultramicroscopy},
title = {Dislocations at coalescence boundaries in heteroepitaxial GaN/sapphire studied after the epitaxial layer has completely coalesced},
year = {2021},
issn = {0304-3991},
month = {December},
pages = {113258},
volume = {231},
abstract = {We have performed cross-sectional scanning capacitance microscopy (SCM), cathodoluminescence (CL) microscopy in the scanning electron microscope (SEM) and transmission electron microscopy (TEM) all on the same few-micron region of a GaN/sapphire sample. To achieve this, it was necessary to develop a process flow which allowed the same features viewed in a cleaved cross-section to be traced from one microscope to the next and to adapt the focused ion beam preparation of the TEM lamella to allow preparation of a site-specific sample on a pre-cleaved cross-section. Growth of our GaN/sapphire samples involved coalescence of three-dimensional islands to form a continuous film. Highly doped marker layers were included in the sample so that coalescence boundaries formed late in the film growth process could be identified in SCM and CL. Using TEM, we then identified one or more dislocations associated with each of several such late-coalescing boundaries. In contrast, previous studies have addressed coalescence boundaries formed earlier in the growth process and have shown that early-stage island coalescence does not lead to dislocation formation.},
doi = {10.1016/j.ultramic.2021.113258},
keywords = {scanning capacitance microscopy, transmission electron microscopy, GaN/sapphire, Physics, Instrumentation, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials},
url = {https://doi.org/10.1016/j.ultramic.2021.113258},
}

@Article{strathprints76944,
author = {Massabuau, F. and Nicol, D. and Adams, F. and Jarman, J. and Roberts, J. and Kov{\'a}cs, A. and Chalker, P. and Oliver, R.},
journal = {Journal of Physics D: Applied Physics},
title = {Study of {Ti} contacts to corundum {α-Ga₂O₃}},
year = {2021},
issn = {0022-3727},
month = {September},
number = {38},
volume = {54},
abstract = {We present a study of the electrical, structural and chemical properties of Ti contacts on atomic layer deposited {\ensuremath{\alpha}}-Ga2O3 film. Ti forms an ohmic contact with {\ensuremath{\alpha}}-Ga2O3. The contact performance is highly dependent on the post-evaporation annealing temperature, where an improved conductivity is obtained when annealing at 450 oC, and a strong degradation when annealing at higher temperatures. Structural and chemical characterisation by transmission electron microscopy techniques reveal that the electrical improvement or degradation of the contact upon annealing can be attributed to oxidation of the Ti metallic layer by the Ga2O3 film in combination with the possibility for Ti diffusion into the Au layer. The results highlight that the grain boundaries and inclusions in the Ga2O3 film provide fast diffusion pathways for this reaction, leaving the {\ensuremath{\alpha}}-Ga2O3 crystallites relatively unaffected - this result differs from previous reports conducted on {\ensuremath{\beta}}-Ga2O3. This study underlines the necessity for a phase-specific and growth method-specific study of contacts on Ga2O3 devices.},
doi = {10.1088/1361-6463/ac0d28},
keywords = {Ti alloys, {\ensuremath{\alpha}}-Ga2O3, atomic layers, Physics, Surfaces, Coatings and Films, Acoustics and Ultrasonics, Electronic, Optical and Magnetic Materials, Condensed Matter Physics},
url = {https://doi.org/10.1088/1361-6463/ac0d28},
}

@Article{strathprints76861,
author = {Holmes, M. J. and Zhu, T. and Massabuau, F. C.-P. and Jarman, J. and Oliver, R. A. and Arakawa, Y.},
journal = {APL Materials},
title = {Pure single photon emission from an {InGaN/GaN} quantum dot},
year = {2021},
issn = {2166-532X},
month = {June},
number = {6},
volume = {9},
abstract = {Single-photon emitters with high degrees of purity are required for photonic-based quantum technologies. InGaN/GaN quantum dots are promising candidates for the development of single-photon emitters but have typically exhibited emission with insufficient purity. Here, pulsed single-photon emission with high purity is measured from an InGaN quantum dot. A raw g(2)(0) value of 0.043 {$\pm$} 0.009 with no corrections whatsoever is achieved under quasi-resonant pulsed excitation. Such a low value is, in principle, sufficient for use in quantum key distribution systems.},
doi = {10.1063/5.0049488},
keywords = {pure, single-photon emission, InGaN/GaN quantum dot, Physics, Physics and Astronomy(all)},
url = {https://doi.org/10.1063/5.0049488},
}

@Article{strathprints76277,
author = {Vacek, Petr and Frentrup, Martin and Lee, Lok Yi and Massabuau, Fabien C.-P. and Kappers, Menno J. and Wallis, David J. and Groger, Roman and Oliver, Rachel A.},
journal = {Journal of Applied Physics},
title = {Defect structures in (001) zincblende {GaN/3C-SiC} nucleation layers},
year = {2021},
issn = {0021-8979},
month = {April},
number = {15},
pages = {155306},
volume = {129},
abstract = {The defect structure of zincblende GaN nucleation layers grown by metalorganic vapor-phase epitaxy on 3C-SiC/Si (001) was investigated by high-resolution scanning transmission electron microscopy. Perfect dislocations, partial dislocations, and stacking faults are present in the layers. Perfect dislocations are identified as 60o mixed-type and act as misfit dislocations to relieve the compressive lattice mismatch strain in GaN. Stacking faults are mainly bounded by 30o Shockley partial dislocations and rarely by Lomer-Cottrell partial dislocations, both of which are able to relieve the compressive lattice mismatch strain in the layer. We propose that the stacking faults and their partial dislocations originate from the dissociation of perfect dislocations present in the zincblende GaN layer and by direct nucleation of partial dislocations loops from the surface. These are the two main mechanisms that lead to the final defect structure of the zincblende GaN nucleation layers.},
doi = {10.1063/5.0036366},
keywords = {defect structures, nucleation, zincblende GaN, electron microscopy, stacking faults, Physics, Optics. Light, Physics and Astronomy(all)},
url = {https://doi.org/10.1063/5.0036366},
}

@InCollection{strathprints75759,
author = {Massabuau, F. C.-P. and Roberts, J. W. and Nicol, D. and Edwards, P. R. and McLelland, M. and Dallas, G. L. and Hunter, D. A. and Nicolson, E. A. and Jarman, J. C. and Kov{\'a}cs, A. and Martin, R. W. and Oliver, R. A. and Chalker, P. R.},
booktitle = {Proceedings Volume 11687, Oxide-based Materials and Devices},
publisher = {Society of Photo-Optical Instrumentation Engineers},
title = {Progress in atomic layer deposited {α-Ga₂O₃} materials and solar-blind detectors},
year = {2021},
address = {Bellingham, WA, United States},
editor = {David J. Rogers and David C. Look and Ferechteh H. Teherani},
isbn = {9781510642096},
month = {March},
note = {{\copyright} 2021 Society of Photo Optical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this publication for a fee or for commercial purposes, and modification of the contents of the publication are prohibited.},
series = {Proceedings of SPIE - The International Society for Optical Engineering},
abstract = {Atomic layer deposition (ALD) offers a low thermal budget method for producing {\ensuremath{\alpha}}-Ga2O3 films on sapphire substrate. In this paper we review the recent progress on plasma-enhanced ALD growth of {\ensuremath{\alpha}}-Ga2O3 and present the optical and photoconductive properties of the deposited films. We show that the deposited material exhibits an epitaxial relationship with the sapphire substrate, and with an atomically sharp film-substrate interface. The {\ensuremath{\alpha}}-Ga2O3 films had an optical bandgap energy measured at 5.11 eV, and exhibited a broad luminescence spectrum dominated by ultraviolet, blue and green bands, in line with current literature. We finally demonstrate the suitability of the material for solar-blind photodetection.},
doi = {10.1117/12.2588729},
keywords = {gallium oxide, corundum phase, atomic layer deposition, solar-blind detection, Optics. Light, Atomic and Molecular Physics, and Optics},
url = {https://doi.org/10.1117/12.2588729},
}

@Article{strathprints76067,
author = {O'Hanlon, T. J. and Massabuau, F. C.-P. and Bao, A. and Kappers, M. J. and Oliver, R. A.},
journal = {Ultramicroscopy},
title = {Directly correlated microscopy of trench defects in {InGaN} quantum wells},
year = {2021},
issn = {0304-3991},
month = {March},
pages = {113255},
volume = {231},
abstract = {Directly correlated measurements of the surface morphology, light emission and subsurface structure and composition were carried out on the exact same nanoscale trench defects in InGaN quantum well (QW) structures. Multiple scanning probe, scanning electron and transmission electron microscopy techniques were used to explain the origin of their unusual emission behaviour and the relationship between surface morphology and cathodoluminescence (CL) redshift. Trench defects comprise of an open trench partially or fully enclosing material in InGaN QWs with different CL emission properties to their surroundings. The CL redshift was shown to typically vary with the width of the trench and the prominence of the material enclosed by the trench above its surroundings. Three defects, encompassing typical and atypical features, were prepared into lamellae for transmission electron microscopy (TEM). A cross marker technique was used in the focused ion beam-scanning electron microscope (FIB-SEM) to centre the previously characterised defects in each lamella for further analysis. The defects with wider trenches and strong redshifts in CL emission had their initiating basal-plane stacking fault (BSF) towards the bottom of the QW stack, while the BSF formed near the top of the QW stack for a defect with a narrow trench and minimal redshift. The raised-centre, prominent defect showed a slight increase in QW thickness moving up the QW stack while QW widths in the level-centred defect remained broadly constant. The indium content of the enclosed QWs increased above the BSF positions up to a maximum, with an increase of approximately 4\% relative to the surroundings seen for one defect examined. Gross fluctuations in QW width (GWWFs) were present in the surrounding material in this sample but were not seen in QWs enclosed by the defect volumes. These GWWFs have been linked with indium loss from surface step edges two or more monolayers high, and many surface step edges appear pinned by the open trenches, suggesting another reason for the higher indium content seen in QWs enclosed by trench defects.},
doi = {10.1016/j.ultramic.2021.113255},
keywords = {Gallium nitride, trench defect, quantum well, multi-microscopy, sample preparation, properties correlation, Physics, Instrumentation, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials},
url = {https://doi.org/10.1016/j.ultramic.2021.113255},
}

@article{strathprints74941,
volume = {11},
number = {12},
month = {December},
title = {Ti alloyed {\ensuremath{\alpha}}-Ga2O3 : route towards wide band gap engineering},
year = {2020},
doi = {10.3390/mi11121128},
journal = {Micromachines},
keywords = {gallium oxide, wide band gap semiconductors, solar-blind detection, atomic layer deposition, thin films, alloying, bandgap, Physics, Physics and Astronomy(all)},
url = {https://doi.org/10.3390/mi11121128},
issn = {2072-666X},
abstract = {The suitability of Ti as a band gap modifier for {\ensuremath{\alpha}}-Ga2O3 was investigated, taking advantage of the isostructural {\ensuremath{\alpha}} phases and high band gap difference between Ti2O3 and Ga2O3. Films of (Ti,Ga)2O3 were synthesized by atomic layer deposition on sapphire substrates, and characterized to determine how crystallinity and band gap vary with composition for this alloy. We report the deposition of high quality {\ensuremath{\alpha}}-(TixGa1-x)2O3 films with x = 3.7\%. For greater compositions the crystalline quality of the films degrades rapidly, where the corundum phase is maintained in films up to x = 5.3\%, and films containing greater Ti fractions being amorphous. Over the range of achieved corundum phase films, that is 0\% {$\leq$} x {$\leq$} 5.3\%, the band gap energy varies by {$\sim$} 270 meV. The ability to maintain a crystalline phase at low fractions of Ti, accompanied by a modification in band gap, shows promising prospects for band gap engineering and the development of wavelength specific solar-blind photodetectors based on {\ensuremath{\alpha}}-Ga2O3.},
author = {Barthel, Armin and Roberts, Joseph and Napari, Mari and Frentrup, Martin and Huq, Tahmida and Kov{\'a}cs, Andr{\'a}s and Oliver, Rachel and Chalker, Paul and Sajavaara, Timo and Massabuau, Fabien}
}

@article{strathprints74634,
volume = {12},
number = {48},
month = {December},
title = {Crystalline interlayers for reducing the effective thermal boundary resistance in GaN-on-diamond},
journal = {ACS Applied Materials and Interfaces},
doi = {10.1021/acsami.0c10129},
pages = {54138--54145},
year = {2020},
keywords = {GaN-on-diamond, thermal boundary resistance, thermal management, GaN, diamond, Physics, Physics and Astronomy(all)},
url = {https://doi.org/10.1021/acsami.0c10129},
issn = {1944-8244},
abstract = {Integrating diamond with GaN high electron mobility transistors (HEMTs) improves thermal management, ultimately increasing the reliability and performance of high-power high-frequency radio frequency amplifiers. Conventionally, an amorphous interlayer is used before growing polycrystalline diamond onto GaN in these devices. This layer contributes significantly to the effective thermal boundary resistance (TBReff) between the GaN HEMT and the diamond, reducing the benefit of the diamond heat spreader. Replacing the amorphous interlayer with a higher thermal conductivity crystalline material would reduce TBReff and help to enable the full potential of GaN-on-diamond devices. In this work, a crystalline Al0.32Ga0.68N interlayer has been integrated into a GaN/AlGaN HEMT device epitaxy. Two samples were studied, one with diamond grown directly on the AlGaN interlayer and another incorporating a thin crystalline SiC layer between AlGaN and diamond. The TBReff, measured using transient thermoreflectance, was improved for the sample with SiC (30 {$\pm$} 5 m2 K GW-1) compared to the sample without (107 {$\pm$} 44 m2 K GW-1). The reduced TBReff is thought to arise from improved adhesion between SiC and the diamond compared to the diamond directly on AlGaN because of an increased propensity for carbide bond formation between SiC and the diamond. The stronger carbide bonds aid transmission of phonons across the interface, improving heat transport.},
author = {Field, Daniel E. and Cuenca, Jerome A. and Smith, Matthew and Fairclough, Simon M. and Massabuau, Fabien C-P and Pomeroy, James W. and Williams, Oliver and Oliver, Rachel A. and Thayne, Iain and Kuball, Martin}
}

@article{strathprints74786,
month = {November},
title = {Thermal stress modelling of diamond on GaN/III-Nitride membranes},
year = {2020},
doi = {10.1016/j.carbon.2020.11.067},
journal = {Carbon},
keywords = {cvd diamond, allium nitride, membranes, thermal stress, finite element modelling, Physics, Chemistry(all)},
url = {https://doi.org/10.1016/j.carbon.2020.11.067},
issn = {0008-6223},
abstract = {Diamond heat-spreaders for gallium nitride (GaN) devices currently depend upon a robust wafer bonding process. Bonding-free membrane methods demonstrate potential, however, chemical vapour deposition (CVD) of diamond directly onto a III-nitride (III-N) heterostructure membrane induces significant thermal stresses. In this work, these thermal stresses are investigated using an analytical approach, a numerical model and experimental validation. The thermal stresses are caused by the mismatch in the coefficient of thermal expansion (CTE) between the GaN/III-N stack, silicon (Si) and the diamond from room temperature to CVD growth temperatures. Simplified analytical wafer bow models underestimate the membrane bow for small sizes while numerical models replicate the stresses and bows with increased accuracy using temperature gradients. The largest tensile stress measured using Raman spectroscopy at room temperature was approximately 1.0 {$\pm$}0.2GPa while surface profilometry shows membrane bows as large as 58{\ensuremath{\mu}}m. This large bow is caused by additional stresses from the Si frame in the initial heating phase which are held in place by the diamond and highlights challenges for any device fabrication using contact lithography. However, the bow can be reduced if the membrane is pre-stressed to become flat at CVD temperatures. In this way, a sufficient platform to grow diamond on GaN/III-N structures without wafer bonding can be realised.},
author = {Cuenca, Jerome A. and Smith, Matthew D. and Field, Daniel E. and Massabuau, Fabien C-P. and Mandal, Soumen and Pomeroy, James and Wallis, David J. and Oliver, Rachel A. and Thayne, Iain and Kuball, Martin and Williams, Oliver A.}
}

@article{strathprints72481,
volume = {167},
month = {October},
title = {Mixed-size diamond seeding for low-thermal-barrier growth of CVD diamond onto GaN and AlN},
year = {2020},
pages = {620--626},
doi = {10.1016/j.carbon.2020.05.050},
journal = {Carbon},
keywords = {chemical vapour deposition (CVD), thermal boundary resistance, transient thermoreflectance (TTR), diamond seeding, Chemistry, Physics, Chemistry(all)},
url = {https://doi.org/10.1016/j.carbon.2020.05.050},
issn = {0008-6223},
abstract = {We report a method of growing a diamond layer via chemical vapour deposition (CVD) utilizing a mixture of microdiamond and nanodiamond seeding to give a low effective thermal boundary resistance (TBR eff) for heat-spreading applications in high-frequency, high-power electronic devices. CVD diamond was deposited onto thin layers of both GaN and AlN on Si substrates, comparing conventional nanodiamond seeding with a two-step process involving sequential seeding with microdiamond then nanodiamond. Thermal properties were determined using transient thermoreflectance (TTR), and the samples were also analysed with SEM and X-ray tomography. While diamond growth directly onto GaN proved to be unsuccessful due to poor adhesion, films grown on AlN were adherent and robust. The two-step mixed-seeding method gave TBR eff values {\ensuremath{<}} 6 m 2 K GW ?1 that were 30 times smaller than for films grown under identical conditions but using nanodiamond seeding alone. Such remarkably low thermal barriers obtained with the mixed-seeding process offer a promising route for fabrication of high-power GaN HEMTs using diamond as a heat spreader with an AlN interlayer.},
author = {Smith, E. J. W. and Piracha, A. H. and Fields, D. and Pomeroy, J. W. and Mackenzie, G. R. and Abdallah, Z. and Massabuau, F. C-P. and Hinz, A. M. and Wallis, D. J. and Oliver, R. A. and Kuball, M. and May, P. W.}
}

@article{strathprints72869,
volume = {12},
month = {August},
title = {Sequential plan-view imaging of sub-surface structures in the transmission electron microscope},
year = {2020},
doi = {10.1016/j.mtla.2020.100798},
note = {Manuscript includes supplementary information.},
journal = {Materialia},
keywords = {transmission electron microscopy (TEM), sample preparation, layered structures, Gallium Nitride, dislocations, Physics, Electronic, Optical and Magnetic Materials},
url = {https://doi.org/10.1016/j.mtla.2020.100798},
issn = {2589-1529},
abstract = {Transmission electron microscopy (TEM) is a central technique for the characterisation of materials at the atomic scale. However, it requires the sample to be thin enough to be electron transparent, imposing strict limitations when studying thick structures in plan-view. Here we present a method for sequential plan-view TEM that allows one to image complex structures at various depths. The approach consists of performing an iterative series of front-side ion milling followed by TEM imaging. We show it is possible to image how the sample properties vary with depth up to several microns below the surface, with no degradation of the sample and imaging conditions throughout the experiment. We apply this approach to 3D cavities in mesoporous GaN distributed Bragg reflectors, demonstrating the ability to characterise the morphology of the pores, local crystal features and chemical composition through the multilayer structure. The same workflow can be applied to a variety of complex micron-scale systems which are by nature too thick for standard TEM analysis, and can also be adapted for profiling samples in cross-section.},
author = {Massabuau, F. C-P. and Springbett, H. P. and Divitini, G. and Griffin, P. H. and Zhu, T. and Oliver, R. A.}
}

@article{strathprints71665,
volume = {212},
month = {May},
title = {Cross-shaped markers for the preparation of site-specific transmission electron microscopy lamellae using focused ion beam techniques},
year = {2020},
doi = {10.1016/j.ultramic.2020.112970},
journal = {Ultramicroscopy},
keywords = {cross-shaped markers, electron microscopy, electron-beam-induced deposition (EBID), FIB-SEM, Physics, Instrumentation, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials},
url = {https://doi.org/10.1016/j.ultramic.2020.112970},
issn = {0304-3991},
abstract = {We describe the use of a cross-shaped platinum marker deposited using electron-beam-induced deposition (EBID) in a focused ion beam - scanning electron microscope (FIB-SEM) system to facilitate site-specific preparation of a TEM foil containing a trench defect in an InGaN/GaN multiple quantum well structure. The defect feature is less than 100 nm wide at the surface. The marker is deposited prior to the deposition of a protective platinum strap (also by EBID) with the centre of the cross indicating the location of the feature of interest, while the arms of the square cross make an acute angle of 45o with the strap's long axis. During the ion-beam thinning process, the marker may be viewed in cross-section from both sides of the sample alternately, and the coming together of the features relating to the arms of the cross indicates increasing proximity to the feature of interest. Although this approach does allow increased precision in locating the region of interest during thinning, it also increases the time required to complete the sample preparation. Hence, this method is particularly well suited to directly correlated multi-microscopy investigations in previously characterised material where high yield and the precise location are more important than preparation time. In addition to TEM lamella preparation, this method could equally be useful for preparing site-specific atom probe tomography (APT) samples.},
author = {O'Hanlon, T. J. and Bao, A. and Massabuau, F. C.-P. and Kappers, M. J. and Oliver, R. A.}
}

@article{strathprints71762,
volume = {8},
number = {3},
month = {March},
title = {Dislocations as channels for the fabrication of sub-surface porous GaN by electrochemical etching},
year = {2020},
doi = {10.1063/1.5142491},
journal = {APL Materials},
keywords = {electrochemical etching, porous nanostructures, electron microscopy, Physics, Physics and Astronomy(all)},
url = {https://doi.org/10.1063/1.5142491},
issn = {2166-532X},
abstract = {Porosification of nitride semiconductors provides a new paradigm for advanced engineering of the properties of optoelectronic materials. Electrochemical etching creates porosity in doped layers whilst leaving undoped layers undamaged, allowing the realisation of complex three-dimensional porous nanostructures, potentially offering a wide range of functionalities, such as in distributed Bragg reflectors. Porous/non-porous multilayers can be formed by etching whole, as-grown wafers uniformly in one simple process, without any additional processing steps. The etch penetrates from the top down, through the undoped layers, leaving them almost untouched. Here, atomic-resolution electron microscopy is used to show that the etchant accesses the doped layers via nanometre-scale channels that form at dislocation cores and transport the etchant and etch products to and from the doped layer respectively. Results on AlGaN and non-polar GaN multilayers indicate the same mechanism is operating, suggesting this approach may be applicable in a range of materials.},
author = {Massabuau, Fabien C.-P. and Griffin, Peter H. and Springbett, Helen P. and Liu, Yingjun and Kumar, R. Vasant and Zhu, Tongtong and Oliver, Rachel A.}
}

@article{strathprints71547,
volume = {10},
number = {3},
month = {March},
title = {GaN-on-diamond technology platform : bonding-free membrane manufacturing process},
year = {2020},
doi = {10.1063/1.5129229},
journal = {AIP Advances},
keywords = {GaN-on-diamond, atomic force microscopy, membrane manufacturing, Physics, Materials Science(all)},
url = {https://doi.org/10.1063/1.5129229},
issn = {2158-3226},
abstract = {GaN-on-diamond samples were demonstrated using a membrane-based technology. This was achieved by selective area Si substrate removal of areas of up to 1 cm {$\times$} 1 cm from a GaN-on-Si wafer, followed by direct growth of a polycrystalline diamond using microwave plasma chemical vapor deposition on etch exposed N-polar AlN epitaxial nucleation layers. Atomic force microscopy and transmission electron microscopy were used to confirm the formation of high quality, void-free AlN/diamond interfaces. The bond between the III-nitride layers and the diamond was validated by strain measurements of the GaN buffer layer. Demonstration of this technology platform is an important step forward for the creation of next generation high power electronic devices.},
author = {Smith, Matthew D. and Cuenca, Jerome A. and Field, Daniel E. and Fu, Yen-chun and Yuan, Chao and Massabuau, Fabien and Mandal, Soumen and Pomeroy, James W. and Oliver, Rachel A. and Uren, Michael J. and Elgaid, Khaled and Williams, Oliver A. and Thayne, Iain and Kuball, Martin}
}

@Article{strathprints71643,
author = {D. Cameron and K. P. O'Donnell and P. R. Edwards and M. Peres and K. Lorenz and M. J. Kappers and M. Bo{\'c}kowski},
journal = {Applied Physics Letters},
title = {Acceptor state anchoring in gallium nitride},
year = {2020},
month = {February},
pages = {102105},
volume = {116},
abstract = {The dual nature of the magnesium acceptor in gallium nitride results in dynamic defect complexes. Europium spectator ions reveal switching between two spectrally unique metastable centres, each corresponding to a particular acceptor state. By ion co-implantation of europium and oxygen into GaN(Mg), we produce, in addition, an anchored state system. In doing so we create an abundance of previously unidentified stable centres which we denote as "Eu0(Ox)". We introduce a microscopic model for these centres with oxygen substituting for nitrogen in the bridging site.},
doi = {10.1063/1.5142168},
keywords = {rare earth (RE) ions, europium, gallium nitride, Physics, Electronic, Optical and Magnetic Materials, Condensed Matter Physics},
url = {https://strathprints.strath.ac.uk/71643/},
}

@article{strathprints70036,
volume = {528},
month = {December},
title = {Low temperature growth and optical properties of {\ensuremath{\alpha}}-Ga2O3 deposited on sapphire by plasma enhanced atomic layer deposition},
year = {2019},
doi = {10.1016/j.jcrysgro.2019.125254},
journal = {Journal of Crystal Growth},
keywords = {characterization, crystal structure, crystal morphology, x-ray diffraction, atomic layer epitaxy, gallium compounds, Physics, Materials Science(all)},
url = {https://doi.org/10.1016/j.jcrysgro.2019.125254},
issn = {0022-0248},
abstract = {Plasma enhanced atomic layer deposition was used to deposit thin films of Ga2O3 on to c-plane sapphire substrates using triethylgallium and O2 plasma. The influence of substrate temperature and plasma processing parameters on the resultant crystallinity and optical properties of the Ga2O3 films were investigated. The deposition temperature was found to have a significant effect on the film crystallinity. At temperatures below 200oC amorphous Ga2O3 films were deposited. Between 250oC and 350oC the films became predominantly {\ensuremath{\alpha}}-Ga2O3. Above 350oC the deposited films showed a mixture of {\ensuremath{\alpha}}-Ga2O3 and {\ensuremath{\epsilon}}-Ga2O3 phases. Plasma power and O2 flow rate were observed to have less influence over the resultant phases present in the films. However, both parameters could be tuned to alter the strain of the film. Ultraviolet transmittance measurements on the Ga2O3 films showed that the bandgaps ranges from 5.0 eV to 5.2 eV with the largest bandgap of 5.2 eV occurring for the {\ensuremath{\alpha}}-Ga2O3 phase deposited at 250oC.},
author = {Roberts, J. W. and Chalker, P. R. and Ding, B. and Oliver, R. A. and Gibbon, J. T. and Jones, L. A. H. and Dhanak, V. R. and Phillips, L. J. and Major, J. D. and Massabuau, F. C.-P.}
}

@article{strathprints70192,
volume = {11},
number = {43},
month = {October},
title = {Thick adherent diamond films on AlN with low thermal barrier resistance},
journal = {ACS Applied Materials and Interfaces},
doi = {10.1021/acsami.9b13869},
pages = {40826--40834},
year = {2019},
keywords = {diamond, aluminium nitride, thermal barrier resistance, diamond seeding, diamond growth, Physics, Materials Science(all), Surfaces and Interfaces},
url = {https://doi.org/10.1021/acsami.9b13869},
issn = {1944-8244},
abstract = {The growth of {\ensuremath{>}}100-{\ensuremath{\mu}}m-thick diamond layers adherent on aluminum nitride with low thermal boundary resistance between diamond and AlN is presented in this work. The thermal barrier resistance was found to be in the range of 16 m 2.K/GW, which is a large improvement on the current state-of-the-art. While thick films failed to adhere on untreated AlN films, AlN films treated with hydrogen/nitrogen plasma retained the thick diamond layers. Clear differences in {\ensuremath{\zeta}}-potential measurement confirm surface modification due to hydrogen/nitrogen plasma treatment. An increase in non-diamond carbon in the initial layers of diamond grown on pretreated AlN is seen by Raman spectroscopy. The presence of non-diamond carbon has minimal effect on the thermal barrier resistance. The surfaces studied with X-ray photoelectron spectroscopy revealed a clear distinction between pretreated and untreated samples. The surface aluminum goes from a nitrogen-rich environment to an oxygen-rich environment after pretreatment. A clean interface between diamond and AlN is seen by cross-sectional transmission electron microscopy.},
author = {Mandal, Soumen and Yuan, Chao and Massabuau, Fabien and Pomeroy, James W. and Cuenca, Jerome and Bland, Henry and Thomas, Evan and Wallis, David and Batten, Tim and Morgan, David and Oliver, Rachel and Kuball, Martin and Williams, Oliver A.}
}

@article{strathprints70116,
month = {October},
title = {Impact of alloy fluctuations and Coulomb effects on the electronic and optical properties of c-plane GaN/AlGaN quantum wells},
year = {2019},
journal = {Scientific Reports},
keywords = {photoluminescence, GaN/AlGaN quantum wells, Physics, Physics and Astronomy(all)},
url = {https://strathprints.strath.ac.uk/70116/},
issn = {2045-2322},
abstract = {We report on a combined theoretical and experimental study of the impact of alloy fluctuations and Coulomb effects on the electronic and optical properties ofc-plane GaN/AlGaN multi-quantum well systems. The presence of carrier localization effects in this system was demonstrated by experimental observations, such as the "S-shape" temperature dependence of the photoluminescence (PL) peak energy, and non-exponential PL decay curves that varied across the PL spectra at 10 K. A three-dimensional modified continuum model, coupled with a self-consistent Hartree scheme, was employed to gain insight into the electronic and optical properties of the experimentally studied c-plane GaN/AlGaN quantum wells. This model confirmedthe existence of strong hole localization arising from the combined effects of the built-in polarization field along the growth direction and the alloy fluctuations at the quantum well/barrier interface. However, for electrons these localization effects are less pronounced in comparison to the holes. Furthermore, our calculations show that the attractive Coulomb interaction between electron and hole results in exciton localization. This behavior is in contrast to the picture of independently localized electrons and holes, often used to explain the radiative recombination process in c-plane InGaN/GaN quantum well systems},
author = {Roble, A. A. and Patra, S. K. and Massabuau, F. and Frentrup, M. and Leontiadou, M. A. and Dawson, P. and Kappers, M. J. and Oliver, R. A. and Graham, D. M. and Schulz, S.}
}

@article{strathprints79377,
volume = {524},
month = {October},
title = {Investigation of MOVPE-grown zincblende GaN nucleation layers on 3CSiC/Si substrates},
year = {2019},
doi = {10.1016/j.jcrysgro.2019.125167},
journal = {Journal of Crystal Growth},
keywords = {atomic force microscopy, nucleation, X-ray diffraction, Metalorganic vapor phase epitaxy, nitrides, semiconducting gallium compounds, Physics, Atomic and Molecular Physics, and Optics},
url = {https://doi.org/10.1016/j.jcrysgro.2019.125167},
issn = {0022-0248},
abstract = {Cubic zincblende (zb-)GaN nucleation layers (NLs) grown by MOVPE on 3C-SiC/Si substrates were studied to determine their optimal thickness for subsequent zb-GaN epilayer growth. The layers were characterised by atomic force microscopy, X-ray diffraction and scanning transmission electron microscopy. The as-grown NLs, with nominal thicknesses varying from 3 nm to 44 nm, consist of small grains which are elongated in the [1 ?1 0] direction, and cover the underlying SiC surface almost entirely. Thermal annealing of the NLs by heating in a H2/NH3 atmosphere to the elevated epilayer growth temperature reduces the substrate coverage of the films that are less than 22 nm thick, due to both material desorption and the ripening of islands. The compressive biaxial in-plane strain of the NLs reduces with increasing NL thickness to the value of relaxed GaN for a thickness of 44 nm. Both the as-grown and annealed NLs are crystalline and have high zincblende phase purity, but contain defects including misfit dislocations and stacking faults. The zb-GaN epilayers grown on the thinnest NLs show an enhanced fraction of the wurtzite phase, most likely formed by nucleation on the exposed substrate surface at elevated temperature, thus dictating the minimum NL thickness for phase-pure zb-GaN epilayer growth.},
author = {Lee, Lok Yi and Frentrup, Martin and Vacek, Petr and Massabuau, Fabien C.-P. and Kappers, Menno J. and Wallis, David J. and Oliver, Rachel A.}
}

@InCollection{strathprints70802,
author = {Fabien C.-P. Massabuau and Jochen Bruckbauer and Carol Trager-Cowan and Rachel A. Oliver},
title = {Microscopy of defects in semiconductors},
booktitle = {Characaterisation and Control of Defects in Semiconductors},
publisher = {IET},
year = {2019},
editor = {Filip Tuomisto},
series = {Materials, Circuits and Devices},
address = {[S.I.]},
month = {September},
abstract = {In this chapter, the authors discuss microscopy techniques that can be useful in addressing defects in semiconductors. They focus on three main families: scanning probe microscopy, scanning electron microscopy and transmission electron microscopy. They first address the basic principles of the selected microscopy techniques In discussions of image formation, they elucidate the mechanisms by which defects are typically imaged in each technique. Then, in the latter part of the chapter, they describe some key examples of the application of microscopy to semiconductor materials, addressing both point and extended defects and both two-dimensional (2D) and three-dimensional (3D) materials.},
keywords = {microscopy, cathodoluminescence, atomic force microscopy, image formation, point defects, scanning electron microscopy, Physics, Atomic and Molecular Physics, and Optics},
url = {https://strathprints.strath.ac.uk/70802/},
}

@article{strathprints69890,
volume = {52},
number = {47},
month = {September},
title = {Atomic layer deposited {\ensuremath{\alpha}}-Ga2O3 solar-blind photodetectors},
year = {2019},
doi = {10.1088/1361-6463/ab3b76},
journal = {Journal of Physics D: Applied Physics},
keywords = {gallium oxide, ultraviolet, photodetector, atomic layer deposition, anneal, Physics, Physics and Astronomy(all)},
url = {https://doi.org/10.1088/1361-6463/ab3b76},
issn = {0022-3727},
abstract = {Low temperature atomic layer deposition was used to deposit {\ensuremath{\alpha}}-Ga2O3 films, which were subsequently annealed at various temperatures and atmospheres. The {\ensuremath{\alpha}}-Ga2O3 phase is stable up to 400 oC, which is also the temperature that yields the most intense and sharpest reflection by x-ray diffraction. Upon annealing at 450 oC and above, the material gradually turns into the more thermodynamically stable {\ensuremath{\epsilon}} or {\ensuremath{\beta}} phase. The suitability of the materials for solar-blind photodetector applications has been demonstrated with the best responsivity achieved being 1.2 A W?1 under 240 nm illumination and 10 V bias, for the sample annealed at 400 oC in argon. It is worth noting however that the device performance strongly depends on the annealing conditions, with the device annealed in forming gas behaving poorly. Given that the tested devices have similar microstructure, the discrepancies in device performance are attributed to hydrogen impurities.},
author = {Moloney, J and Tesh, O and Singh, M and Roberts, J W and Jarman, J C and Lee, L C and Huq, T N and Brister, J and Karboyan, S and Kuball, M and Chalker, P R and Oliver, R A and Massabuau, F C-P}
}

@Article{strathprints67565,
author = {F.C-P. Massabuau and M.K. Horton and E. Pearce and S. Hammersley and P. Chen and M.S. Zielinski and T. Weatherley and G. Divitini and P.R. Edwards and M.J. Kappers and C. McAleese and M.A. Moram and C.J. Humphreys and P. Dawson and R.A. Oliver},
title = {Optical and structural properties of dislocations in InGaN},
journal = {Journal of Applied Physics},
year = {2019},
volume = {125},
pages = {165701},
month = {April},
abstract = {Threading dislocations in thick layers of InₓGa₁₋ₓN (5% < x < 15%) have been investigated by means of cathodoluminescence, time-resolved cathodoluminescence and molecular dynamics. We show that indium atoms segregate near dislocations in all the samples. This promotes the formation of In-N-In chains and atomic condensates which localize carriers and hinder non-radiative recombination at dislocations. We note however that the dark halo surrounding the dislocations in the cathodoluminescence image becomes increasingly pronounced as the indium fraction of the sample increases. Using transmission electron microscopy, we attribute the dark halo to a region of lower indium content formed below the facet of the V-shaped pit that terminates the dislocation in low composition samples (x < 12%). For x > 12%, the facets of the V-defect featured dislocation bundles instead of the low indium fraction region. In this sample the origin of the dark halo may relate to a compound effect of the dislocation bundles, of a variation of surface potential and perhaps of an increase in carrier diffusion length.},
keywords = {indium gallium nitride, cathodoluminescence, transmission electron microscopy, Physics, Physics and Astronomy(all)},
url = {https://strathprints.strath.ac.uk/67565/}
}

@Article{strathprints65532,
author = {Paul R. Edwards and Kevin P. O'Donnell and Akhilesh K. Singh and Douglas Cameron and Katharina Lorenz and Mitsuo Yamaga and Jacob H. Leach and Menno J. Kappers and Michal Bo{\'c}kowski},
title = {Hysteretic photochromic switching (HPS) in doubly doped GaN(Mg):Eu{--}a summary of recent results},
journal = {Materials},
year = {2018},
volume = {11},
number = {10},
pages = {1800},
month = {September},
abstract = {Europium is the most-studied and least-well-understood rare earth ion (REI) dopant in GaN. While attempting to increase the efficiency of red GaN light-emitting diodes (LEDs) by implanting Eu+ into p-type GaN templates, the Strathclyde University group, in collaboration with IST Lisbon and Unipress Warsaw, discovered hysteretic photochromic switching (HPS) in the photoluminescence spectrum of doubly doped GaN(Mg):Eu. Our recent work, summarised in this contribution, has used time-, temperature- and light-induced changes in the Eu intra-4f shell emission spectrum to deduce the microscopic nature of the Mg-Eu defects that form in this material. As well as shedding light on the Mg acceptor in GaN, we propose a possible role for these emission centres in quantum information and computing.},
keywords = {gallium nitride, rare earth ions, europium, photoluminescence, photochromism, qubit, Physics, Materials Science(all), Physics and Astronomy(all)},
url = {https://strathprints.strath.ac.uk/65532/}
}

@article{strathprints79475,
volume = {11},
number = {10},
month = {September},
note = {This article belongs to the Special Issue III-Nitrides Semiconductor Research in the UK and Ireland},
title = {Characterisation of InGaN by photoconductive atomic force microscopy},
journal = {Materials},
doi = {10.3390/ma11101794},
year = {2018},
keywords = {InGaN, photoconductive atomic force microscopy, dislocations, Mining engineering. Metallurgy, Materials Science(all)},
url = {https://doi.org/10.3390/ma11101794},
issn = {1996-1944},
abstract = {Nanoscale structure has a large effect on the optoelectronic properties of InGaN, a material vital for energy saving technologies such as light emitting diodes. Photoconductive atomic force microscopy (PC-AFM) provides a new way to investigate this effect. In this study, PC-AFM was used to characterise four thick ({$\sim$}130 nm) In x Ga 1?x N films with x = 5\%, 9\%, 12\%, and 15\%. Lower photocurrent was observed on elevated ridges around defects (such as V-pits) in the films with x{$\leq$}12 \%. Current-voltage curve analysis using the PC-AFM setup showed that this was due to a higher turn-on voltage on these ridges compared to surrounding material. To further understand this phenomenon, V-pit cross sections from the 9\% and 15\% films were characterised using transmission electron microscopy in combination with energy dispersive X-ray spectroscopy. This identified a subsurface indium-deficient region surrounding the V-pit in the lower indium content film, which was not present in the 15\% sample. Although this cannot directly explain the impact of ridges on turn-on voltage, it is likely to be related. Overall, the data presented here demonstrate the potential of PC-AFM in the field of III-nitride semiconductors.},
author = {Weatherley, Thomas F. K. and Massabuau, Fabien C.-P. and Kappers, Menno J. and Oliver, Rachel A.}
}

@article{strathprints79480,
volume = {11},
number = {1736},
month = {September},
note = {This article belongs to the Special Issue III-Nitrides Semiconductor Research in the UK and Ireland},
title = {Effects of a Si-doped InGaN underlayer on the optical properties of InGaN/GaN quantum well structures with different numbers of QuantumWells},
journal = {Materials},
doi = {10.3390/ma11091736},
year = {2018},
keywords = {effects, Si-doped InGaN underlayer, optical properties, InGaN/GaN, quantum well structures, quantum wells, Physics, Materials Science(all)},
url = {https://doi.org/10.3390/ma11091736},
issn = {1996-1944},
abstract = {In this paper we report on the optical properties of a series of InGaN polar quantum well structures where the number of wells was 1, 3, 5, 7, 10 and 15 and which were grown with the inclusion of an InGaN Si-doped underlayer. When the number of quantum wells is low then the room temperature internal quantum efficiency can be dominated by thermionic emission from the wells. This can occur because the radiative recombination rate in InGaN polar quantum wells can be low due to the built-in electric field across the quantum well which allows the thermionic emission process to compete effectively at room temperature limiting the internal quantum efficiency. In the structures that we discuss here, the radiative recombination rate is increased due to the effects of the Si-doped underlayer which reduces the electric field across the quantum wells. This results in the effect of thermionic emission being largely eliminated to such an extent that the internal quantum efficiency at room temperature is independent of the number of quantum wells.},
author = {Christian, George and Kappers, Menno and Massabuau, Fabien and Humphreys, Colin and Oliver, Rachel and Dawson, Philip}
}

@article{strathprints79474,
volume = {24},
number = {S1},
month = {August},
title = {Atomic resolution imaging of dislocations in algan and the efficiency of UV LEDs},
journal = {Microscopy and Microanalysis},
doi = {10.1017/S143192761800051X},
pages = {4--5},
year = {2018},
keywords = {atomic resolution imaging, dislocations, AIGaN, efficiency, UV LEDs, Mining engineering. Metallurgy, Materials Science(all)},
url = {https://doi.org/10.1017/S143192761800051X},
issn = {1431-9276},
abstract = {{{[}}Abstract not available]},
author = {Humphreys, Colin J. and Massabuau, Fabien C-P. and Rhode, Sneha L. and Horton, Matthew K. and O'Hanlon, Thomas J. and Kovacs, Andras and Zielinski, Marcin S. and Kappers, Menno J. and Dunin-Borkowski, Rafal E. and Oliver, Rachel A.}
}

@Article{strathprints79478,
author = {Church, S. A. and Hammersley, S. and Mitchell, P. W. and Kappers, M. J. and Lee, L. Y. and Massabuau, F. and Sahonta, S. L. and Frentrup, M. and Shaw, L. J. and Wallis, D. J. and Humphreys, C. J. and Oliver, R. A. and Binks, D. J. and Dawson, P.},
journal = {Journal of Applied Physics},
title = {Effect of stacking faults on the photoluminescence spectrum of zincblende GaN},
year = {2018},
issn = {0021-8979},
month = {May},
volume = {123},
abstract = {The photoluminescence spectra of a zincblende GaN epilayer grown via metal-organic chemical vapour deposition upon 3C-SiC/Si (001) substrates were investigated. Of particular interest was a broad emission band centered at 3.4 eV, with a FWHM of 200 meV, which extends above the bandgap of both zincblende and wurtzite GaN. Photoluminescence excitation measurements show that this band is associated with an absorption edge centered at 3.6 eV. Photoluminescence time decays for the band are monoexponential, with lifetimes that reduce from 0.67 ns to 0.15 ns as the recombination energy increases. TEM measurements show no evidence of wurtzite GaN inclusions which are typically used to explain emission in this energy range. However, dense stacking fault bunches are present in the epilayers. A model for the band alignment at the stacking faults was developed to explain this emission band, showing how both electrons and holes can be confined adjacent to stacking faults. Different stacking fault separations can change the carrier confinement energies sufficiently to explain the width of the emission band, and change the carrier wavefunction overlap to account for the variation in decay time.},
doi = {10.1063/1.5026267},
keywords = {effect, stacking faults, photoluminescence spectrum, zincblende GaN, Physics, Physics and Astronomy(all)},
url = {https://doi.org/10.1063/1.5026267},
}

@article{strathprints69863,
volume = {487},
month = {April},
title = {{\ensuremath{\alpha}}-Ga2O3 grown by low temperature atomic layer deposition on sapphire},
year = {2018},
pages = {23--27},
doi = {10.1016/j.jcrysgro.2018.02.014},
journal = {Journal of Crystal Growth},
keywords = {semiconducting gallium compounds, oxides, atomic layer epitaxy, x-ray diffraction, scanning electron diffraction, Physics, Physics and Astronomy(all)},
url = {https://doi.org/10.1016/j.jcrysgro.2018.02.014},
issn = {0022-0248},
abstract = {{\ensuremath{\alpha}}-Ga2O3 is a metastable phase of Ga2O3 of interest for wide bandgap engineering since it is isostructural with {\ensuremath{\alpha}}-In2O3 and {\ensuremath{\alpha}}-Al2O3. {\ensuremath{\alpha}}-Ga2O3 is generally synthesised under high pressure (several GPa) or relatively high temperature ({$\sim$}500 oC). In this study, we report the growth of {\ensuremath{\alpha}}-Ga2O3 by low temperature atomic layer deposition (ALD) on sapphire substrate. The film was grown at a rate of 0.48 {\AA}/cycle, and predominantly consists of {\ensuremath{\alpha}}-Ga2O3 in the form of -oriented columns originating from the interface with the substrate. Some inclusions were also present, typically at the tips of the {\ensuremath{\alpha}} phase columns and most likely comprising {\ensuremath{\epsilon}}-Ga2O3. The remainder of the Ga2O3 film - i.e. nearer the surface and between the {\ensuremath{\alpha}}-Ga2O3 columns, was amorphous. The film was found to be highly resistive, as is expected for undoped material. This study demonstrates that {\ensuremath{\alpha}}-Ga2O3 films can be grown by low temperature ALD and suggests the possibility of a new range of ultraviolet optoelectronic and power devices grown by ALD. The study also shows that scanning electron diffraction is a powerful technique to identify the different polymorphs of Ga2O3 present in multiphase samples.},
author = {Roberts, J. W. and Jarman, J. C. and Johnstone, D. N. and Midgley, P. A. and Chalker, P. R. and Oliver, R. A. and Massabuau, F. C-P.}
}

@incollection{strathprints79473,
volume = {10532},
month = {February},
series = {Proceedings of SPIE - The International Society for Optical Engineering},
booktitle = {Proceedings Volume 10532, Gallium Nitride Materials and Devices XIII},
address = {USA},
title = {Alloy fluctuations at dislocations in III-nitrides : dentification and impact on optical properties},
publisher = {Society of Photo-Optical Instrumentation Engineers},
year = {2018},
doi = {10.1117/12.2288211},
pages = {301--306},
keywords = {dislocation, III-Nitrides, segregation, carrier localization, aberration-corrected TEM, cathodoluminescence, Mining engineering. Metallurgy, Metals and Alloys},
url = {https://doi.org/10.1117/12.2288211},
abstract = {We investigated alloy fluctuations at dislocations in III-Nitride alloys (InGaN and AlGaN). We found that in both alloys, atom segregation (In segregation in InGaN and Ga segregation in AlGaN) occurs in the tensile part of dislocations with an edge component. In InGaN, In atom segregation leads to an enhanced formation of In-N chains and atomic condensates which act as carrier localization centers. This feature results in a bright spot at the position of the dislocation in the CL images, suggesting that non-radiative recombination at dislocations is impaired. On the other hand, Ga atom segregation at dislocations in AlGaN does not seem to noticeably affect the intensity recorded by CL at the dislocation. This study sheds light on why InGaN-based devices are more resilient to dislocations than AlGaN-based devices. An interesting approach to hinder non-radiative recombination at dislocations may therefore be to dope AlGaN with In.},
author = {Massabuau, F. C.-P. and Chen, P. and Rhode, S. L. and Horton, M. K. and O'Hanlon, T. J. and Kov{\'a}cs, A. and Zielinski, M. S. and Kappers, M. J. and Dunin-Borkowski, R. E. and Humphreys, C. J. and Oliver, R. A.}
}

@Article{strathprints62516,
author = {A.K. Singh and K.P. O'Donnell and P.R. Edwards and D. Cameron and K. Lorenz and M.J. Kappers and M. Bo{\'c}kowski and M. Yamaga and R. Prakash},
title = {Luminescence of Eu³⁺ in GaN(Mg, Eu) : transitions from the ⁵D₁ level},
journal = {Applied Physics Letters},
year = {2017},
volume = {111},
pages = {241105},
month = {November},
abstract = {Eu-doped GaN(Mg) exemplifies hysteretic photochromic switching between two configurations, Eu0 and Eu1(Mg), of the same photoluminescent defect. Using above bandgap excitation, we studied the temperature dependence of photoluminescence (TDPL) of transitions from the excited ⁵D₁ level of Eu³⁺ for both configurations of this defect. During sample cooling, ⁵D₁→⁷F₀,₁,₂ transitions of Eu0 manifest themselves at temperatures below ~200 K, while those of Eu1(Mg) appear only during switching. The observed line positions verify crystal field energies of the ⁷F₀,₁,₂ levels. TDPL profiles of ⁵D₁→⁷F₁ and ⁵D₀→7FJ transitions of Eu0 show an onset of observable emission from the ⁵D₁ level coincident with the previously observed, but hitherto unexplained, decrease in the intensity of its ⁵D₀→⁷FJ emission on cooling below 200 K. Hence the ⁵D₀→⁷FJ TDPL anomaly signals a back-up of ⁵D₁ population due to a reduction in phonon-assisted relaxation between ⁵D₁ and ⁵D₀ levels at lower temperatures. We discuss this surprising result in the light of temperature-dependent transient luminescence measurements of Eu0.},
keywords = {photoluminescence, bandgap, temperature, Physics, Physics and Astronomy(all)},
url = {https://strathprints.strath.ac.uk/62516/}
}

@article{strathprints79425,
volume = {50},
number = {433002},
month = {September},
title = {X-ray diffraction analysis of cubic zincblende III-nitrides},
year = {2017},
pages = {1--13},
journal = {Journal of Physics D: Applied Physics},
keywords = {x-ray diffraction, cubic GaN, gallium nitride, phase analysis, green gap problem, LED-based light systems, zincblende GaN thin films, Physics, Surfaces, Coatings and Films, Acoustics and Ultrasonics, Electronic, Optical and Magnetic Materials, Condensed Matter Physics},
url = {https://strathprints.strath.ac.uk/79425/},
issn = {0022-3727},
abstract = {Solving the green gap problem is a key challenge for the development of future LED-based light systems. A promising approach to achieve higher LED efficiencies in the green spectral region is the growth of III-nitrides in the cubic zincblende phase. However, the metastability of zincblende GaN along with the crystal growth process often lead to a phase mixture with the wurtzite phase, high mosaicity, high densities of extended defects and point defects, and strain, which can all impair the performance of light emitting devices. X-ray diffraction (XRD) is the main characterization technique to analyze these device-relevant structural properties, as it is very cheap in comparison to other techniques and enables fast feedback times. In this review, we will describe and apply various XRD techniques to identify the phase purity in predominantly zincblende GaN thin films, to analyze their mosaicity, strain state, and wafer curvature. The different techniques will be illustrated on samples grown by metalorganic vapor phase epitaxy on pieces of 4'' SiC/Si wafers. We will discuss possible issues, which may arise during experimentation, and provide a critical view on the common theories.},
author = {Frentrup, Martin and Lee, Lok Ye and Sahonta, Suman-Lata and Kappers, Menno J. and Massabuau, Fabien and Gupta, Priti and Oliver, Rachel A. and Humphreys, Colin J. and Wallis, David J.}
}

@article{strathprints69879,
volume = {17},
number = {8},
month = {August},
note = {his document is the Accepted Manuscript version of a Published Work that appeared in final form in Nano Letters, copyright {\copyright} American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.nanolett.7b01697.},
title = {Dislocations in AlGaN: core structure, atom segregation, and optical properties},
year = {2017},
journal = {Nano Letters},
doi = {10.1021/acs.nanolett.7b01697},
pages = {4846--4852},
keywords = {AlGaN, InGaN, dislocation, aberration-corrected TEM, cathodoluminescence, Physics, Physics and Astronomy(all)},
url = {https://doi.org/10.1021/acs.nanolett.7b01697},
issn = {1530-6992},
abstract = {We conducted a comprehensive investigation of dislocations in Al0.46Ga0.54N. Using aberration-corrected scanning transmission electron microscopy and energy dispersive X-ray spectroscopy, the atomic structure and atom distribution at the dislocation core have been examined. We report that the core configuration of dislocations in AlGaN is consistent with that of other materials in the III-Nitride system. However, we observed that the dissociation of mixed-type dislocations is impeded by alloying GaN with AlN, which is confirmed by our experimental observation of Ga and Al atom segregation in the tensile and compressive parts of the dislocations, respectively. Investigation of the optical properties of the dislocations shows that the atom segregation at dislocations has no significant effect on the intensity recorded by cathodoluminescence in the vicinity of the dislocations. These results are in contrast with the case of dislocations in In0.09Ga0.91N where segregation of In and Ga atoms also occurs but results in carrier localization limiting non-radiative recombination at the dislocation. This study therefore sheds light on why InGaN-based devices are generally more resilient to dislocations than their AlGaN-based counterparts.},
author = {Massabuau, Fabien C-P. and Rhode, Sneha L. and Horton, Matthew K. and O'Hanlon, Thomas J. and Kovacs, Andras and Zielinski, Marcin S. and Kappers, Menno J. and Dunin-Borkowski, Rafal E. and Humphreys, Colin J. and Oliver, Rachel A.}
}

@article{strathprints79424,
volume = {254},
number = {8},
month = {May},
title = {Mechanisms preventing trench defect formation in InGaN/GaN quantum well structures using hydrogen during GaN barrier growth},
year = {2017},
journal = {Physica Status Solidi B},
keywords = {III-nitrides, epitaxy, hydrogen, trench defect, trench defect formation, quantum well structures, H2, InGaN/GaN quantum well structures, Physics, Electronic, Optical and Magnetic Materials, Condensed Matter Physics},
url = {https://strathprints.strath.ac.uk/79424/},
issn = {0370-1972},
abstract = {Here, we study the mechanisms underlying a method used to limit the formation of trench defects in InGaN/GaN quantum well structures by using H2 in the carrier gas for the growth of GaN barriers. The method leads to a complete removal of the trench defects by preventing the formation of basal-plane stacking faults from which trench defects originate, as well as preventing the formation of stacking mismatch boundaries. The penalty paid for the absence of trench defects is the formation of InGaN wells with gross well-width fluctuations where the H2 gas has etched away the indium locally. Where a fully formed trench defect (stacking mismatch boundary opened as V-shaped ditch) already exists in the structure, the GaN barrier growth method using H2 results in a strongly disturbed structure of the quantum well stack in the enclosed region, with the quantum wells and barriers being in places significantly thinner than their counterparts in the surrounding material.},
author = {Massabuau, Fabien and Kappers, Menno and Humphreys, Colin and Oliver, Rachel}
}

@Article{strathprints60877,
author = {J. T. Griffiths and C. X. Ren and P.-M. Coulon and E. D. Le Boulbar and C. G. Bryce and I. Girgel and A. Howkins and I. Boyd and R. W. Martin and D. W. E. Allsopp and P. A. Shields and C. J. Humphreys and R. A. Oliver},
title = {Structural impact on the nanoscale optical properties of InGaN core-shell nanorods},
journal = {Applied Physics Letters},
year = {2017},
volume = {110},
pages = {172105},
month = {April},
abstract = {III-nitride core-shell nanorods are promising for the development of high efficiency light emitting diodes and novel optical devices. We reveal the nanoscale optical and structural properties of core-shell InGaN nanorods formed by combined top-down etching and regrowth to achieve non-polar sidewalls with a low density of extended defects. While the luminescence is uniform along the non-polar {1-100} sidewalls, nano-cathodoluminescence shows a sharp reduction in the luminescent intensity at the intersection of the non-polar {1-100} facets. The reduction in the luminescent intensity is accompanied by a reduction in the emission energy localised at the apex of the corners. Correlative compositional analysis reveals an increasing indium content towards the corner except at the apex itself. We propose that the observed variations in the structure and chemistry are responsible for the changes in the optical properties at the corners of the nanorods. The insights revealed by nano-cathodoluminescence will aid in the future development of higher efficiency core-shell nanorods.},
keywords = {nanorods, light emitting diodes, nano-cathodoluminescence, nitride semiconductors, quantum confined Stark effect, efficiency droop, Optics. Light, Physics and Astronomy (miscellaneous)},
url = {http://strathprints.strath.ac.uk/60877/}
}

@Article{strathprints60823,
author = {S Magalh{\~a}es and N Franco and I M Watson and R W Martin and K P O'Donnell and H P D Schenk and F Tang and T C Sadler and M J Kappers and R A Oliver and T Monteiro and T L Martin and P A J Bagot and M P Moody and E Alves and K Lorenz},
journal = {Journal of Physics D: Applied Physics},
title = {Validity of Vegard's rule for {AlₓIn₁₋ₓN (0.08 < x < 0.28)} thin films grown on GaN templates},
year = {2017},
month = {April},
note = {This is an author-created, un-copyedited version of an article accepted for publication in Journal of Physics D: Applied Physics. The publisher is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://doi.org/10.1088/1361-6463/aa69dc},
number = {20},
pages = {205107},
volume = {50},
abstract = {In this work, comparative x-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) measurements allow a comprehensive characterization of AlₓIn₁₋ₓN thin films grown on GaN. Within the limits of experimental accuracy, and in the compositional range 0.08  <  x <  0.28, the lattice parameters of the alloys generally obey Vegard's rule, varying linearly with the InN fraction. Results are also consistent with the small deviation from linear behaviour suggested by Darakchieva et al (2008 Appl. Phys. Lett. 93 261908). However, unintentional incorporation of Ga, revealed by atom probe tomography (APT) at levels below the detection limit for RBS, may also affect the lattice parameters. Furthermore, in certain samples the compositions determined by XRD and RBS differ significantly. This fact, which was interpreted in earlier publications as an indication of a deviation from Vegard's rule, may rather be ascribed to the influence of defects or impurities on the lattice parameters of the alloy. The wide-ranging set of AlₓIn₁₋ₓN films studied allowed furthermore a detailed investigation of the composition leading to lattice-matching of AlₓIn₁₋ₓN/GaN bilayers.},
keywords = {comparative x-ray diffraction, Rutherford backscattering spectrometry, Vegard's rule, lattice parameters, gallium, thin films, Physics, Surfaces, Coatings and Films, Acoustics and Ultrasonics, Electronic, Optical and Magnetic Materials, Condensed Matter Physics},
url = {http://strathprints.strath.ac.uk/60823/},
}

@Article{strathprints59627,
author = {Coulon, Pierre-Marie and Shahrzad Hosseini Vajargah and An Bao and Paul R. Edwards and Le Boulbar, Emmanuel D. and Ionut G{\^i}rgel and Robert W. Martin and Colin J. Humphreys and Rachel A. Oliver and Duncan W. E. Allsopp and Philip A. Shields},
title = {Evolution of the m-plane quantum well morphology and composition within a {GaN/InGaN} core-shell structure},
journal = {Crystal Growth and Design},
year = {2017},
volume = {17},
number = {2},
pages = {474--482},
month = {February},
abstract = {GaN/InGaN core-shell nanorods are promising for optoelectronic applications due to the absence of polarization-related electric fields on the sidewalls, a lower defect density, a larger emission volume and strain relaxation at the free surfaces. The core-shell geometry allows the growth of thicker InGaN shell layers, which would benefit the efficiency of light emitting diodes. However, the growth mode of such layers by metal organic vapor phase epitaxy is poorly understood. Through a combination of nanofabrication, epitaxial growth and detailed characterization, this work reveals an evolution in the growth mode of InGaN epitaxial shells, from a two dimensional (2D) growth mode to three dimensional (3D) striated growth without additional line defect formation with increasing layer thickness. Measurements of the indium distribution show fluctuations along the {\ensuremath{<}}10-10{\ensuremath{>}} directions, with low and high indium composition associated with the 2D and 3D growth modes, respectively. Atomic steps at the GaN/InGaN core-shell interface were observed to occur with a similar frequency as quasi-periodic indium fluctuations along [0001] observed within the 2D layer, to provide evidence that the resulting local strain relief at the steps acts as the trigger for a change of growth mode by elastic relaxation. This study demonstrates that misfit dislocation generation during the growth of wider InGaN shell layers can be avoided by using pre-etched GaN nanorods. Significantly, this enables the growth of absorption-based devices and light-emitting diodes with emissive layers wide enough to mitigate efficiency droop.},
keywords = {nanorod, core-shell, InGaN, m-plane, morphology, AFM, TEM, EDX, nanofabrication, epitaxial growth, Chemistry, Physics, Materials Science(all), Chemistry(all), Condensed Matter Physics},
url = {http://strathprints.strath.ac.uk/59627/}
}

@Article{strathprints59279,
author = {A. K. Singh and K. P. O'Donnell and P. R. Edwards and K. Lorenz and M. J. Kappers and M. Bo{\'c}kowski},
title = {Hysteretic photochromic switching of {Eu-Mg} defects in {GaN} links the shallow transient and deep ground states of the {Mg} acceptor},
journal = {Scientific Reports},
year = {2017},
volume = {7},
pages = {41982},
month = {February},
abstract = {Although p-type activation of GaN by Mg underpins a mature commercial technology, the nature of the Mg acceptor in GaN is still controversial. Here, we use implanted Eu as a `spectator ion' to probe the lattice location of Mg in doubly doped GaN(Mg):Eu. Photoluminescence spectroscopy of this material exemplifies hysteretic photochromic switching (HPS) between two configurations, Eu0 and Eu1(Mg), of the same Eu-Mg defect, with a hyperbolic time dependence on `switchdown' from Eu0 to Eu1(Mg). The sample temperature and the incident light intensity at 355 nm tune the characteristic switching time over several orders of magnitude, from less than a second at 12.5 K, ~100 mW/cm2 to (an estimated) several hours at 50 K, 1 mW/cm². Linking the distinct Eu-Mg defect configurations with the shallow transient and deep ground states of the Mg acceptor in the Lany-Zunger model, we determine the energy barrier between the states to be 27.7(4) meV, in good agreement with the predictions of theory. The experimental results further suggest that at low temperatures holes in deep ground states are localized on N atoms axially bonded to Mg acceptors.},
keywords = {photoluminescence spectroscopy, hysteretic photochromic switching, Lany-Zunger model, energy barrier, shallow transient state, deep ground state, acceptor state, Physics, Physics and Astronomy(all)},
url = {http://strathprints.strath.ac.uk/59279/}
}

@article{strathprints69871,
volume = {121},
number = {1},
month = {January},
note = {This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Massabuau, F, Chen, P, Horton, MK, Rhode, SL, Ren, CX, O'Hanlon, TJ, Kovacs, A, Kappers, MJ, Humphreys, CJ, Dunin-Borkowski, RE \& Oliver, RA 2017, 'Carrier localization in the vicinity of dislocations in InGaN' Journal of Applied Physics, vol. 121, no. 013104 and may be found at https://doi.org/10.1063/1.4973278.},
title = {Carrier localization in the vicinity of dislocations in InGaN},
journal = {Journal of Applied Physics},
doi = {10.1063/1.4973278},
year = {2017},
keywords = {materials science, atomic force microscopy, chemical elements, luminescence, Monte Carlo methods, semiconductors, Physics, Physics and Astronomy(all)},
url = {https://doi.org/10.1063/1.4973278},
issn = {0021-8979},
abstract = {We present a multi-microscopy study of dislocations in InGaN, whereby the same threading dislocation was observed under several microscopes (atomic force microscopy, scanning electron microscopy, cathodoluminescence imaging and spectroscopy, transmission electron microscopy), and its morphological optical and structural properties directly correlated. We achieved this across an ensemble of defects large enough to be statistically significant. Our results provide evidence that carrier localization occurs in the direct vicinity of the dislocation through the enhanced formation of In-N chains and atomic condensates, thus limiting non-radiative recombination of carriers at the dislocation core. We highlight that the localization properties in the vicinity of threading dislocations arise as a consequence of the strain field of the individual dislocation and the additional strain field building between interacting neighboring dislocations. Our study therefore suggests that careful strain and dislocation distribution engineering may further improve the resilience of InGaN-based devices to threading dislocations. Besides providing a new understanding of dislocations in InGaN, this paper presents a proof-of-concept for a methodology which is relevant to many problems in materials science.},
author = {Massabuau, F. C-P. and Chen, P. and Horton, M. K. and Rhode, S. L. and Ren, C. X. and O'Hanlon, T. J. and Kov{\'a}cs, A. and Kappers, M. J. and Humphreys, C. J. and Dunin-Borkowski, R. E. and Oliver, R. A.}
}

@article{strathprints79426,
volume = {254},
number = {8},
month = {January},
title = {X-ray reflectivity method for the characterization of InGaN/GaN quantum well interface},
year = {2017},
journal = {Physica Status Solidi B},
keywords = {III-nitride semiconductors, GaN, InGaN, interfaces, quantum wells, X-ray reflectivity, interface roughness, gross well width fluctuations, compositional fluctuations, Physics, Electronic, Optical and Magnetic Materials, Condensed Matter Physics},
url = {https://strathprints.strath.ac.uk/79426/},
issn = {0370-1972},
abstract = {A method to characterize the interface of InGaN/GaN quantum wells by X-ray reflectivity is presented. The interface roughness can be obtained from the ratio of diffuse to specular scatterings obtained on a transverse urn:x-wiley:15213951:media:pssb201600664:pssb201600664-math-0001-scan. Rotation around the azimuthal urn:x-wiley:15213951:media:pssb201600664:pssb201600664-math-0002 angle allows for information about the directionality of the roughening mechanisms to be obtained. The method allows for quick identification of the presence or absence of gross well width fluctuations in the quantum well, providing that the interface is chemically sharp. When the interface exhibits chemical grading, compositional fluctuations across the terraced structure of the quantum well surface lead to aggravated roughness as the barrier is grown, which may be misinterpreted as gross well width fluctuations. This method carries promises for complementing analysis by transmission electron microscopy as it is non-destructive, fast, and allows multi-directional characterization of the roughness. It would therefore be particularly useful to detect process deviation in a production line, where prior knowledge of the sample is already available.},
author = {Massabuau, Fabien and Piot, Nicolas and Frentrup, Martin and Wang, Xiuze and Avenas, Quentin and Kappers, Menno and Humphreys, Colin and Oliver, Rachel}
}

@article{strathprints79375,
volume = {13},
number = {5-6},
month = {May},
title = {Room temperature PL efficiency of InGaN/GaN quantum well structures with prelayers as a function of number of quantum wells},
journal = {Physica Status Solidi C},
doi = {10.1002/pssc.201510180},
pages = {248--251},
year = {2016},
keywords = {indium gallium nitride, InGaN, quantum wells, prelayer, underlayer, Physics, Physics and Astronomy (miscellaneous)},
url = {https://doi.org/10.1002/pssc.201510180},
issn = {1610-1642},
abstract = {We report on the effects of varying the number of quantum wells (QWs) in an InGaN/GaN multiple QW (MQW) structure containing a 23 nm thick In0.05Ga0.95N prelayer doped with Si. The calculated conduction and valence bands for the structures show an increasing total electric field across the QWs with increasing number of QWs. This is due to the reduced strength of the surface polarisation field, which opposes the built-in field across the QWs, as its range is increased over thicker samples. Low temperature photoluminescence (PL) measurements show a red shifted QW emission peak energy, which is attributed to the enhanced quantum confined Stark effect with increasing total field strength across the QWs. Low temperature PL time decay measurements and room temperature internal quantum efficiency (IQE) measurements show decreasing radiative recombination rates and decreasing IQE, respectively, with increasing number of QWs. These are attributed to the increased spatial separation of the electron and hole wavefunctions, consistent with the calculated band profiles. It is also shown that, for samples with fewer QWs, the reduction of the total field across the QWs makes the radiative recombination rate sufficiently fast that it is competitive with the efficiency losses associated with the thermal escape of carriers.},
author = {Christian, George M. and Hammersley, Simon and Davies, Matthew J. and Dawson, Philip and Kappers, Menno J. and Massabuau, Fabien C.-P. and Oliver, Rachel A. and Humphreys, Colin J.}
}

@article{strathprints79436,
volume = {13},
number = {5-6},
month = {February},
title = {Effect of electron blocking layers on the conduction and valence band profiles of InGaN/GaN LEDs},
year = {2016},
pages = {262--265},
journal = {Physica Status Solidi C},
keywords = {LEDs, electron blocking layers, efficiency, photoluminescence, valence band profiles, quantum well active region, Physics, Condensed Matter Physics},
url = {https://strathprints.strath.ac.uk/79436/},
issn = {1610-1642},
abstract = {In this paper we investigate the effect of including an electron blocking layer between the quantum well active region and the p-type layers of a light emitting diode has on the conduction and valence band profile of a light emitting diode. Two light emitting diode structures with nominally identical quantum well active regions one containing an electron blocking layer and one without were grown for the purposes of this investigation. The conduction and valence band profiles for both structures were then calculated using a commercially available Schr{\"o}dinger-Poisson calculator, and a modification to the electric field across the QWs observed. The results of these calculations were then compared to photoluminescence and photoluminescence time decay measurements. The modification in electric field across the quantum wells of the structures resulted in slower radiative recombination in the sample containing an electron blocking layers. The sample containing an electron blocking layer was also found to exhibit a lower internal quantum efficiency, which we attribute to the observed slower radiative recombination lifetime making radiative recombination less competitive.},
author = {Hammersley, Simon and Daswson, Phil and Kappers, Menno J. and Massabuau, Fabien C.-P. and Frentrup, Martin and Oliver, Rachel A. and Humphreys, Colin J.}
}

@article{strathprints79432,
volume = {119},
number = {5},
month = {February},
title = {A comparison of the optical properties of InGaN/GaN multiple quantum well structures grown with and without Si-doped InGaN prelayers},
year = {2016},
journal = {Journal of Applied Physics},
keywords = {optical properties, InGaN/GaN, multiple quantum well structures, InGaN prelayers, spectroscopic study, photoluminescence, Stark effect, Physics, Physics and Astronomy(all)},
url = {https://strathprints.strath.ac.uk/79432/},
issn = {0021-8979},
abstract = {In this paper, we report on a detailed spectroscopic study of the optical properties of InGaN/GaN multiple quantum well structures, both with and without a Si-doped InGaN prelayer. In photoluminescence and photoluminescence excitation spectroscopy, a 2nd emission band, occurring at a higher energy, was identified in the spectrum of the multiple quantum well structure containing the InGaN prelayer, originating from the first quantum well in the stack. Band structure calculations revealed that a reduction in the resultant electric field occurred in the quantum well immediately adjacent to the InGaN prelayer, therefore leading to a reduction in the strength of the quantum confined Stark effect in this quantum well. The partial suppression of the quantum confined Stark effect in this quantum well led to a modified (higher) emission energy and increased radiative recombination rate. Therefore, we ascribed the origin of the high energy emission band to recombination from the 1st quantum well in the structure. Study of the temperature dependent recombination dynamics of both samples showed that the decay time measured across the spectrum was strongly influenced by the 1st quantum well in the stack (in the sample containing the prelayer) leading to a shorter average room temperature lifetime in this sample. The room temperature internal quantum efficiency of the prelayer containing sample was found to be higher than the reference sample (36\% compared to 25\%) which was thus attributed to the faster radiative recombination rate of the 1st quantum well providing a recombination pathway that is more competitive with non-radiative recombination processes.},
author = {Davies, M. J. and Hammersley, S and Massabuau, F. C.-P. and Dawson, P and Oliver, R. A. and Kappers, M. J. and Humphreys, C. J.}
}

@article{strathprints79433,
volume = {13},
number = {5-6},
month = {February},
title = {Effect of QW growth temperature on the optical properties of blue and green InGaN/GaN QW structures},
year = {2016},
pages = {209--213},
journal = {Physica Status Solidi C},
keywords = {green gap, InGaN, quantum wells, efficiency, photoluminescence, Physics, Condensed Matter Physics},
url = {https://strathprints.strath.ac.uk/79433/},
issn = {1610-1642},
abstract = {In this paper we report on the impact that the quantum well growth temperature has on the internal quantum efficiency and carrier recombination dynamics of two sets of InGaN/GaN multiple quantum well samples, designed to emit at 460 and 530 nm, in which the indium content of the quantum wells within each sample set was maintained. Measurements of the internal quantum efficiency of each sample set showed a systematic variation, with quantum wells grown at a higher temperature exhibiting higher internal quantum efficiency and this variation was preserved at all excitation power densities. By investigating the carrier dynamics at both 10 K and 300 K we were able to attribute this change in internal quantum efficiency to a decrease in the non-radiative recombination rate as the QW growth temperature was increased which we attribute to a decrease in incorporation of the point defects.},
author = {Hammersley, Simon and Kappers, Menno J. and Massabuau, Fabien C.-P. and Sahonta, Suman-Lata and Dawson, Phil and Oliver, Rachel A. and Humphreys, Colin J.}
}

@Article{strathprints55347,
author = {K. P. O'Donnell and P. R. Edwards and M. Yamaga and K. Lorenz and M. J. Kappers and M. Bo{\'c}kowski},
title = {Crystalfield symmetries of luminescent {Eu³⁺} centers in {GaN} : the importance of the {⁵D₀} to {⁷F₁} transition},
journal = {Applied Physics Letters},
year = {2016},
volume = {108},
number = {2},
pages = {022102},
month = {January},
abstract = {Eu-doped GaN is a promising material with potential application not only in optoelectronics but also in magneto-optical and quantum optical devices ?beyond the light emitting diode?. Its interesting spectroscopy is unfortunately complicated by spectral overlaps due to ?site multiplicity?, the existence in a given sample of multiple composite centers in which Eu ions associate with intrinsic or extrinsic defects. We show here that elementary crystalfield analysis of the 5D0 to 7F1 transition can critically distinguish such sites. Hence, we find that the center involved in the hysteretic photochromic switching (HPS) observed in GaN(Mg):Eu, proposed as the basis of a new solid state qubit material, is not in fact Eu1, as previously reported, but a related defect, Eu1(Mg). Furthermore, the decomposition of the crystalfield distortions of Eu0, Eu1(Mg) and Eu1 into axial and non-axial components strongly suggests reasonable microscopic models for the defects themselves.},
keywords = {crystal defects, III-V semiconductors, visible spectra, rare earth ions, emission spectra, Physics, Condensed Matter Physics, Electronic, Optical and Magnetic Materials},
url = {http://strathprints.strath.ac.uk/55347/}
}

@Article{strathprints56455,
author = {C.X. Ren and B. Rouet-Leduc and J.T. Griffiths and E. Bohacek and M.J. Wallace and P.R. Edwards and M.A. Hopkins and D.W.E. Allsopp and M.J. Kappers and R.W. Martin and R.A. Oliver},
title = {Analysis of defect-related inhomogeneous electroluminescence in {InGaN/GaN QW LED}s},
journal = {Superlattices and Microstructures},
year = {2016},
volume = {99},
pages = {118--124},
abstract = {The inhomogeneous electroluminescence (EL) of InGaN/GaN quantum well light emitting diode structures was investigated in this study. Electroluminescence hyperspectral images showed that inhomogeneities in the form of bright spots exhibited spectrally blue-shifted and broadened emission. Scanning electron microscopy combined with cathodoluminescence (SEM-CL) was used to identify hexagonal pits at the centre of approximately 20\% of these features. Scanning transmission electron microscopy imaging with energy dispersive X-ray spectroscopy (STEM-EDX) indicated there may be p-doped AlGaN within the active region caused by the presence of the pit. Weak beam dark-field TEM (WBDF-TEM) revealed the presence of bundles of dislocations associated with the pit, suggesting the surface features which cause the inhomogeneous EL may occur at coalescence boundaries, supported by trends in the number of features observed across the wafer.},
keywords = {semiconductor, LED, defect, electroluminescence, Physics, Physics and Astronomy(all)},
url = {http://strathprints.strath.ac.uk/56455/}
}

@article{strathprints79441,
volume = {107},
number = {132106},
month = {October},
title = {Effects of quantum well growth temperature on the recombination efficiency of InGaN/GaN multiple quantum wells that emit in the green and blue spectral regions},
year = {2015},
journal = {Applied Physics Letters},
keywords = {quantum well growth temperature, InGaN/GaN, recombination efficiency, multiple quantum wells, light emitting diodes, green spectral region, photoluminescence spectroscopy, quantum efficiency, Physics, Physics and Astronomy (miscellaneous)},
url = {https://strathprints.strath.ac.uk/79441/},
issn = {0003-6951},
abstract = {nGaN-based light emitting diodes and multiple quantum wells designed to emit in the green spectral region exhibit, in general, lower internal quantum efficiencies than their blue-emitting counter parts, a phenomenon referred to as the "green gap." One of the main differences between green-emitting and blue-emitting samples is that the quantum well growth temperature is lower for structures designed to emit at longer wavelengths, in order to reduce the effects of In desorption. In this paper, we report on the impact of the quantum well growth temperature on the optical properties of InGaN/GaN multiple quantum wells designed to emit at 460 nm and 530 nm. It was found that for both sets of samples increasing the temperature at which the InGaN quantum well was grown, while maintaining the same indium composition, led to an increase in the internal quantum efficiency measured at 300 K. These increases in internal quantum efficiency are shown to be due reductions in the non-radiative recombination rate which we attribute to reductions in point defect incorporation.},
author = {Hammersley, S and Kappers, M. J. and Massabuau, F. C.-P. and Sahonta, S and Dawson, P and Oliver, R. A. and Humphreys, C. J.}
}

@article{strathprints79439,
volume = {252},
number = {5},
month = {May},
title = {A study of the inclusion of prelayers in InGaN/GaN single- and multiple-quantum-well structures},
journal = {Physica Status Solidi B},
doi = {10.1002/pssb.201451535},
pages = {866--872},
year = {2015},
keywords = {GaN, InGan, photoluminescence, quantum wells, thin films, Physics, Electronic, Optical and Magnetic Materials, Condensed Matter Physics},
url = {https://doi.org/10.1002/pssb.201451535},
issn = {0370-1972},
abstract = {We report on the effects on the optical properties of blue-light emitting InGaN/GaN single- and multiple-quantum-well structures including a variety of prelayers. For each single-quantum-well structure containing a Si-doped prelayer, we measured a large blue shift of the photoluminescence peak energy and a significant increase in radiative recombination rate at 10 K. Calculations of the conduction and valence band energies show a strong reduction in the built-in electric field across the quantum well (QW) occurs when including Si-doped prelayers, due to enhancement of the surface polarization field which opposes the built-in field. The reduction in built-in field across the QW results in an increase in the electron-hole wavefunction overlap, increasing the radiative recombination rate, and a reduction in the strength of the quantum confined Stark effect, leading to the observed blue shift of the emission peak. The largest reduction of the built-in field occurred for an InGaN:Si prelayer, in which the additional InGaN/GaN interface of the prelayer, in close proximity to the QW, was shown to further reduce the built-in field. Study of multiple QW structures with and without an InGaN:Si prelayer showed the same mechanisms identified in the equivalent single-quantum-well structure.},
author = {Davies, Matthew J. and Dawson, Philip and Massabuau, Fabien C.-P. and Le Fol, Adrian and Oliver, Rachel A. and Kappers, Menno J. and Humphreys, Colin J.}
}

@article{strathprints79443,
volume = {106},
number = {7},
month = {February},
title = {Indium clustering in a-plane InGaN quantum wells as evidenced by atom probe tomography},
year = {2015},
journal = {Applied Physics Letters},
keywords = {Indium clustering, a-plane InGaN quantum wells, atom probe tomography, electron beams, quantum wells, x-ray diffraction, Physics, Physics and Astronomy (miscellaneous)},
url = {https://strathprints.strath.ac.uk/79443/},
issn = {0003-6951},
abstract = {Atom probe tomography (APT) has been used to characterize the distribution of In atoms within non-polar a-plane InGaN quantum wells (QWs) grown on a GaN pseudo-substrate produced using epitaxial lateral overgrowth. Application of the focused ion beam microscope enabled APT needles to be prepared from the low defect density regions of the grown sample. A complementary analysis was also undertaken on QWs having comparable In contents grown on polar c-plane sample pseudo-substrates. Both frequency distribution and modified nearest neighbor analyses indicate a statistically non-randomized In distribution in the a-plane QWs, but a random distribution in the c-plane QWs. This work not only provides insights into the structure of non-polar a-plane QWs but also shows that APT is capable of detecting as-grown nanoscale clustering in InGaN and thus validates the reliability of earlier APT analyses of the In distribution in c-plane InGaN QWs which show no such clustering.},
author = {Tang, Fengzai and Zhu, Tongtong and Oehler, Fabrice and Fu, Wai Yuen and Griffiths, James T. and Massabuau, Fabien C. -P. and Kappers, Menno J. and Martin, Tomas L. and Bagot, Paul A. J. and Moody, Michael P. and Oliver, Rachel A.}
}

@Article{strathprints52285,
author = {M. J. Wallace and P. R. Edwards and M. J. Kappers and M. A. Hopkins and F. Oehler and S. Sivaraya and R. A. Oliver and C. J. Humphreys and D. W. E. Allsopp and R. W. Martin},
title = {Effect of the barrier growth mode on the luminescence and conductivity micron scale uniformity of {InGaN} light emitting diodes},
journal = {Journal of Applied Physics},
year = {2015},
volume = {117},
number = {11},
pages = {115705},
abstract = {In this paper we present a combined cathodoluminescence and electron beam induced current study of the optical and electrical properties of InGaN LEDs grown using different active region growth methods. In one device, both the quantum wells and quantum barriers were deposited at their optimum temperatures (2T) whereas in the other device, each barrier was grown in a two step process, with the first few nanometers at a lower temperature (Q2T). It was found that, in the Q2T sample, small micron scale domains of lower emission intensity correlate strongly to a lower EBIC signal, whereas in the 2T sample which has a more uniform emission pattern and an anti-correlation exists between CL emission intensity and EBIC signal.},
keywords = {cathodoluminescence, light emitting diode, electron beams, Physics, Physics and Astronomy(all)},
url = {http://strathprints.strath.ac.uk/52285/}
}

@article{strathprints79445,
volume = {252},
number = {5},
month = {December},
title = {Investigation of unintentional indium incorporation into GaN barriers of InGaN/GaN quantum well structures},
year = {2014},
pages = {928--935},
journal = {Physica Status Solidi B},
keywords = {unintentional indium, GaN, indium, InGaN, quantum well structures, segregation, transmission electron microscopy, GaN barriers, Physics, Electronic, Optical and Magnetic Materials, Condensed Matter Physics},
url = {https://strathprints.strath.ac.uk/79445/},
issn = {0370-1972},
abstract = {High resolution transmission electron microscopy has been employed to investigate the impact of the GaN barrier growth technique on the composition profile of InGaN quantum wells (QWs). We show that the profiles deviate from their nominal configuration due to the presence of an indium tail at the upper interface of the QW. This indium tail, thought to be associated with a segregation effect from the indium surfactant layer, has been shown to strongly depend on the growth method. The effect of this tail has been investigated using a self-consistent Schr{\"o}dinger-Poisson simulation. For the simulated conditions, a graded upper interface has been found to result in a decreased electron-hole wavefunction overlap of up to 31\% compared to a QW with a rectangular profile, possibly leading to a decrease in radiative-recombination rate. Therefore, in order to maximize the efficiency of a QW structure, it is important to grow the active region using a growth method which leads to QW interfaces which are as abrupt as possible. The results of this experiment find applications in every study where the emission properties of a device are correlated to a particular active region design.},
author = {Massabuau, F. C.-P. and Davies, M. J. and Blenkhorn, W. E. and Hammersley, S and Kappers, M. J. and Humphreys, C. J. and Dawson, P and Oliver, R. A.}
}

@Article{strathprints49409,
author = {C. Trager-Cowan and G. Naresh-Kumar and N. Allehiani and S. Kraeusel and B. Hourahine and S. Vespucci and D. Thomson and J. Bruckbauer and G. Kusch and P. R. Edwards and R. W. Martin and C. Mauder and A. P. Day and A. Winkelmann and A. Vilalta-Clemente and A. J. Wilkinson and P. J. Parbrook and M. J. Kappers and M. A. Moram and R. A. Oliver and C. J. Humphreys and P. Shields and E. D. Le Boulbar and D. Maneuski and V. O'Shea and K. P. Mingard},
title = {Electron channeling contrast imaging of defects in {III}-nitride semiconductors},
journal = {Microscopy and Microanalysis},
year = {2014},
volume = {20},
number = {S3},
pages = {1024--1025},
month = {August},
keywords = {Physics, Instrumentation},
url = {http://strathprints.strath.ac.uk/49409/}
}

@Article{strathprints47513,
author = {K.P. O'Donnell and P.R. Edwards and M.J. Kappers and K. Lorenz and E.J. Alves and M.X. Bo{\'c}kowski},
title = {Europium-doped {GaN(Mg)} : beyond the limits of the light-emitting diode},
journal = {Physica Status Solidi C},
year = {2014},
volume = {11},
number = {3--4},
pages = {662--665},
month = {April},
abstract = {Rare-earth doped III-N semiconductors have been studied for decades on account of their possible application in visible light-emitting diodes (LED) with built-in utility as red (e.g. Eu), green (Er) and blue (Tm) monochromatic sources (O'Donnell and Dierolf (eds.), Topics in Applied Physics, Vol. 124 (Springer, Dordrecht, 2010) [1]). However, to date, no commercial devices have been introduced on the basis of these materials. Recently, we discovered thermally activated hysteresis in the emission spectrum of p-type GaN thin films that were co-doped with Mg and Eu (O'Donnell et al., Proc. ICPS31, Zurich, July 2012 [2]). We have also reported an unexpected Zeeman splitting and induced magnetic moment of Eu3+ ions in GaN (Kachkanov et al., Scientific Rep. 2, 969 (2012) and MRS Proc. 1290?i03?06 (2011) [3, 4]). These findings encourage speculation on taking the study of RE-doped III-N beyond the limited goal of improving LED efficiency into the realm of novel magneto-optic and quantum-optical devices. In particular we will describe in this presentation the spectroscopy of ion-implanted and annealed GaN(Mg): Eu samples and the possible exploitation of the Mg acceptor in GaN as a qubit.},
keywords = {GaN, rare earth doping, luminescence hysteresis, qubit, Physics, Condensed Matter Physics},
url = {http://strathprints.strath.ac.uk/47513/}
}

@Article{strathprints47167,
author = {Jochen Bruckbauer and Paul R Edwards and Suman-Lata Sahonta and Fabien C-P Massabuau and Menno J Kappers and Colin J Humphreys and Rachel A Oliver and Robert W Martin},
journal = {Journal of Physics D: Applied Physics},
title = {Cathodoluminescence hyperspectral imaging of trench-like defects in {InGaN/GaN} quantum well structures},
year = {2014},
month = {March},
number = {13},
pages = {135107},
volume = {47},
abstract = {Optoelectronic devices based on the III-nitride system exhibit remarkably good optical efficiencies despite suffering from a large density of defects. In this work we use cathodoluminescence (CL) hyperspectral imaging to study InGaN/GaN multiple quantum well (MQW) structures. Different types of trench defects with varying trench width, namely wide or narrow trenches forming closed loops and open loops, are investigated in the same hyperspectral CL measurement. A strong redshift (90 meV) and intensity increase of the MQW emission is demonstrated for regions enclosed by wide trenches, whereas those within narrower trenches only exhibit a small redshift (10 meV) and a slight reduction of intensity compared with the defect-free surrounding area. Transmission electron microscopy (TEM) showed that some trench defects consist of a raised central area, which is caused by an increase of about 40\% in the thickness of the InGaN wells. The causes of the changes in luminescences are also discussed in relation to TEM results identifying the underlying structure of the defect. Understanding these defects and their emission characteristics is important for further enhancement and development of light-emitting diodes.},
keywords = {cathodoluminescence, hyperspectral imaging, trench-like defects, nGaN/GaN, quantum well structures, Physics, Solid state physics. Nanoscience, Surfaces, Coatings and Films, Acoustics and Ultrasonics, Electronic, Optical and Magnetic Materials, Condensed Matter Physics},
url = {http://strathprints.strath.ac.uk/47167/},
}

@article{strathprints46655,
volume = {20},
number = {1},
month = {February},
author = {G. Naresh-Kumar and J. Bruckbauer and P. R. Edwards and S. Kraeusel and B. Hourahine and R. W. Martin and M. J. Kappers and M. A. Moram and S. Lovelock and R. A. Oliver and C. J. Humphreys and C. Trager-Cowan},
title = {Coincident electron channeling and cathodoluminescence studies of threading dislocations in GaN},
journal = {Microscopy and Microanalysis},
pages = {55--60},
year = {2014},
keywords = {electron channeling, cathodoluminescence studies, threading, dislocations, GaN, Instrumentation},
url = {http://strathprints.strath.ac.uk/46655/},
abstract = {We combine two scanning electron microscopy techniques to investigate the influence of dislocations on the light emission from nitride semiconductors. Combining electron channeling contrast imaging and cathodoluminescence imaging enables both the structural and luminescence properties of a sample to be investigated without structural damage to the sample. The electron channeling contrast image is very sensitive to distortions of the crystal lattice, resulting in individual threading dislocations appearing as spots with black?white contrast. Dislocations giving rise to nonradiative recombination are observed as black spots in the cathodoluminescence image. Comparison of the images from exactly the same micron-scale region of a sample demonstrates a one-to-one correlation between the presence of single threading dislocations and resolved dark spots in the cathodoluminescence image. In addition, we have also obtained an atomic force microscopy image from the same region of the sample, which confirms that both pure edge dislocations and those with a screw component (i.e., screw and mixed dislocations) act as nonradiative recombination centers for the Si-doped c-plane GaN thin film investigated.}
}

@article{strathprints79460,
volume = {386},
number = {88},
month = {January},
title = {The impact of substrate miscut on the microstructure and photoluminescence efficiency of (0001) InGaN quantum wells grown by a two-temperature method},
year = {2014},
pages = {88--93},
journal = {Journal of Crystal Growth},
keywords = {metalorganic vapour phase epitaxy, Semiconducting III-V materials, quantum wells, nitrides, two-temperature method, Physics, Materials Chemistry, Inorganic Chemistry, Condensed Matter Physics},
url = {https://strathprints.strath.ac.uk/79460/},
issn = {0022-0248},
abstract = {The impact of the miscut of a (0001) c-plane substrate on the structural and optical properties of InGaN/GaN quantum wells grown by metal-organic vapour phase epitaxy using a two-temperature method has been investigated. The two-temperature growth method involves exposure of the uncapped InGaN quantum well to a temperature ramp in an ammonia atmosphere before growth of the GaN barrier at a higher temperature. The resulting quantum well, consists of interlinking InGaN strips containing gaps which may impede carrier diffusion to dislocations. By increasing the substrate misorientation from 0o to 0.5o we show that the density of InGaN strips increases while the strip width reduces. Our data show that the PL efficiency increases with miscut and that the peak efficiency occurs at a lower excitation power density.},
author = {Massabuau, F. C.-P. and Tartan, C. C. and Traynier, R and Blenkhorn, W. E. and Kappers, M. J. and Dawson, P and Humphreys, C. J. and Oliver, R. A.}
}

@Article{strathprints48986,
author = {M. J. Wallace and P. R. Edwards and M. J. Kappers and M. A. Hopkins and F. Oehler and S. Sivaraya and D. W. E. Allsopp and R. A. Oliver and C. J. Humphreys and R. W. Martin},
journal = {Journal of Applied Physics},
title = {Bias dependence and correlation of the cathodoluminescence and electron beam induced current from an InGaN/GaN light emitting diode},
year = {2014},
number = {3},
pages = {033105},
volume = {116},
abstract = {Micron-scale mapping has been employed to study a contacted InGaN/GaN LED using combined electroluminescence (EL), cathodoluminescence (CL), and electron beam induced current (EBIC). Correlations between parameters, such as the EBIC and CL intensity, were studied as a function of applied bias. The CL and EBIC maps reveal small areas, 2?10 {\ensuremath{\mu}}m in size, which have increased nonradiative recombination rate and/or a lower conductivity. The CL emission from these spots is blue shifted, by 30?40 meV. Increasing the reverse bias causes the size of the spots to decrease, due to competition between in-plane diffusion and drift in the growth direction. EL mapping shows large bright areas ({$\sim$}100 {\ensuremath{\mu}}m) which also have increased EBIC, indicating domains of increased conductivity in the p and/or n-GaN.},
keywords = {bias dependence, cathodoluminescence, electron beam induced current, InGaN/GaN, micron-scale mapping, light emitting diode, electroluminescence, Optics. Light, Atomic and Molecular Physics, and Optics},
url = {http://strathprints.strath.ac.uk/48986/},
}

@article{strathprints79530,
volume = {471},
month = {November},
title = {Towards a better understanding of trench defects in InGaN/GaN quantum wells},
year = {2013},
doi = {10.1088/1742-6596/471/1/012042},
journal = {Journal of Physics: Conference Series},
keywords = {trench defects, quantum wells, InGaN/GaN, transmission electron microscopy, atomic force microscopy, cathodoluminescence, emission properties, Physics, Physics and Astronomy(all)},
url = {https://doi.org/10.1088/1742-6596/471/1/012042},
issn = {1742-6588},
abstract = {Trench defects are a commonly occurring feature in InGaN/GaN quantum well (QW) structures. This defect appears at the surface of a structure as a trench enclosing a region of material with peculiar emission properties. Transmission electron microscopy was used to characterise the sub-surface structure of such defect. It consists of a basal-plane stacking fault (BSF) located in the QW stack and bound by a vertical stacking mismatch boundary (SMB) which runs towards the surface and which opens up into pits, which merge to form a trench. Atomic force microscopy and cathodoluminescence were performed on the same individual defects in order to directly correlate the morphology with the emission properties. A strong correlation has been established between the thickness of the trench and the redshift and intensity of the emission of the enclosed region suggesting that bright trench defects emitting at a longer wavelength nucleate early during the growth. Data also suggest that the SMB may act as a non-radiative recombination centre.},
author = {Massabuau, F C-P and Trinh-Xuan, L and Lodi{\'e}, D and Sahonta, S-L and Rhode, S and Thrush, E J and Oehler, F and Kappers, M J and Humphreys, C J and Oliver, R A}
}

@Article{strathprints43861,
author = {E Taylor and F Fang and F Oehler and P R Edwards and M J Kappers and K Lorenz and E Alves and C McAleese and C J Humphreys and R W Martin},
title = {Composition and luminescence studies of InGaN epilayers grown at different hydrogen flow rates},
journal = {Semiconductor Science and Technology},
year = {2013},
volume = {28},
number = {6},
pages = {065011},
month = {May},
abstract = {Indium gallium nitride (In(x)Ga(1-x)N) is a technologically important material for many optoelectronic devices, including LEDs and solar cells, but it remains a challenge to incorporate high levels of InN into the alloy while maintaining sample quality. A series of InGaN epilayers was grown with different hydrogen flow rates (0-200 sccm) and growth temperatures (680-750 ?C) to obtain various InN fractions and bright emission in the range 390-480 nm. These 160-nm thick epilayers were characterized through several compositional techniques (wavelength dispersive x-ray spectroscopy, x-ray diffraction, Rutherford backscattering spectrometry) and cathodoluminescence hyperspectral imaging. The compositional analysis with the different techniques shows good agreement when taking into account compositional gradients evidenced in these layers. The addition of small amounts of hydrogen to the gas flow at lower growth temperatures is shown to maintain a high surface quality and luminescence homogeneity. This allowed InN fractions of up to {\texttt{\char126}}16\% to be incorporated with minimal peak energy variations over a mapped area while keeping a high material quality.},
keywords = {composition and luminescence studies, InGaN epilayers, hydrogen flow rates, optoelectronic devices, Physics, Materials Chemistry, Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering, Condensed Matter Physics},
url = {http://strathprints.strath.ac.uk/43861/}
}

@article{strathprints10020,
volume = {32},
number = {1-2},
title = {Two-photon absorption from single InGaN/GaN quantum dots},
author = {A.F. Jarjour and A.M. Green and T.J. Parker and R.A. Taylor and R.A. Oliver and G.A.D. Briggs and M.J. Kappers and C.J. Humphreys and R.W. Martin and I.M. Watson},
year = {2006},
pages = {119--122},
journal = {Physica E: Low-dimensional Systems and Nanostructures},
keywords = {InGaN, quantum dot, two-photon absorption, photoluminescence, time-resolved, photoluminescence excitation, Physics, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials, Condensed Matter Physics},
url = {http://strathprints.strath.ac.uk/10020/},
abstract = {We present a study of the time-integrated and time-resolved photoluminescence properties of single-InGaN/GaN quantum dots (QDs) using two-photon spectroscopy. Two samples containing QDs produced by different growth techniques are examined. We find that two-photon excitation results in the suppression of the emission from the underlying quantum well to which the QDs are coupled and yet relatively strong QD emission is observed. This effect is explained in terms of the enhancement of two-photon absorption in QDs due to the full confinement of carriers. Furthermore, evidence of the presence of excited states is revealed from the two-photon photoluminescence excitation spectra presented in the study.}
}