The Semiconductor Spectroscopy and Devices research group is part of the Nanoscience division of the Department of Physics at the University of Strathclyde. The Department is a member of the Scottish Universities Physics Alliance (SUPA).

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Latest publications
A complete list of our papers can be found here.

  • A. K. Singh, K. P. O’Donnell, P. R. Edwards, K. Lorenz, J. H. Leach, and M. Boćkowski, “Eu-Mg defects and donor-acceptor pairs in GaN : photodissociation and the excitation transfer problem,” Journal of Physics D: Applied Physics, vol. 51, p. 65106, 2018.
    [BibTeX] [Abstract] [Download PDF]

    We have investigated temperature-dependent photoluminescence (TDPL) profiles of Eu³⁺ ions implanted in an HVPE-grown bulk GaN sample doped with Mg and of donor-acceptor pairs (DAP) involving the shallow Mg acceptor in GaN(Mg) (unimplanted) and GaN(Mg):Eu samples. Below 125 K, the TDPL of Eu³⁺ in GaN(Mg):Eu correlates with that of the DAP. Below 75 K, the intensity of Eu³⁺ emission saturates, indicating a limitation of the numbers of Eu-Mg defects available to receive excitation transferred from the host, while the DAP continues to increase, albeit more slowly in the implanted than the unimplanted sample. Prolonged exposure to UV light at low temperature results in the photodissociation of Eu-Mg defects, in their Eu1(Mg) configuration, with a corresponding increase in shallow DAP emission and the emergence of emission from unassociated EuGa (Eu2) defects.

    @Article{strathprints62526,
    author = {A.K. Singh and K.P. O'Donnell and P.R. Edwards and K. Lorenz and J.H. Leach and M. Bo{\'c}kowski},
    title = {Eu-Mg defects and donor-acceptor pairs in GaN : photodissociation and the excitation transfer problem},
    journal = {Journal of Physics D: Applied Physics},
    year = {2018},
    volume = {51},
    pages = {065106},
    month = {December},
    abstract = {We have investigated temperature-dependent photoluminescence (TDPL) profiles of Eu³⁺ ions implanted in an HVPE-grown bulk GaN sample doped with Mg and of donor-acceptor pairs (DAP) involving the shallow Mg acceptor in GaN(Mg) (unimplanted) and GaN(Mg):Eu samples. Below 125 K, the TDPL of Eu³⁺ in GaN(Mg):Eu correlates with that of the DAP. Below 75 K, the intensity of Eu³⁺ emission saturates, indicating a limitation of the numbers of Eu-Mg defects available to receive excitation transferred from the host, while the DAP continues to increase, albeit more slowly in the implanted than the unimplanted sample. Prolonged exposure to UV light at low temperature results in the photodissociation of Eu-Mg defects, in their Eu1(Mg) configuration, with a corresponding increase in shallow DAP emission and the emergence of emission from unassociated EuGa (Eu2) defects.},
    keywords = {temperature-dependent photoluminescence, photodissociation, Physics, Physics and Astronomy(all)},
    url = {https://strathprints.strath.ac.uk/62526/}
    }

  • B. Hourahine, D. McArthur, and F. Papoff, “Principal modes of Maxwell’s equations,” in The Generalized Multipole Technique for Light Scattering, T. Wriedt and Y. Eremin, Eds., Berlin: Springer International Publishing AG, 2018.
    [BibTeX] [Abstract] [Download PDF]

    This chapter reviews the use of principal modes–states which are maximally correlated between two subspaces and hence form pairs unique up to phase factors–in solving Maxwell’s equations and analysing these solutions for nanoparticles and structures. The mathematical structure of this method allows a computationally efficient generalisation of Mie’s analytical approach for the sphere to obtain semi-analytical solutions for general geometries with smooth interfaces. We apply this method to investigate a range of single and multiple particle metallic structures in the linear, non-linear and non-local response regimes outside of the quasi-static limit.

    @InCollection{strathprints63767,
    author = {Benjamin Hourahine and Duncan McArthur and Francesco Papoff},
    title = {Principal modes of Maxwell's equations},
    booktitle = {The Generalized Multipole Technique for Light Scattering},
    publisher = {Springer International Publishing AG},
    year = {2018},
    editor = {Thomas Wriedt and Yuri Eremin},
    series = {Springer Series on Atomic, Optical, and Plasma Physics},
    address = {Berlin},
    month = {April},
    abstract = {This chapter reviews the use of principal modes--states which are maximally correlated between two subspaces and hence form pairs unique up to phase factors--in solving Maxwell's equations and analysing these solutions for nanoparticles and structures. The mathematical structure of this method allows a computationally efficient generalisation of Mie's analytical approach for the sphere to obtain semi-analytical solutions for general geometries with smooth interfaces. We apply this method to investigate a range of single and multiple particle metallic structures in the linear, non-linear and non-local response regimes outside of the quasi-static limit.},
    keywords = {principal modes, phase factors, Maxwell's equations, Physics, Mathematics, Mathematics(all), Physics and Astronomy(all)},
    url = {https://strathprints.strath.ac.uk/63767/}
    }

  • C. Brasser, J. Bruckbauer, Y. P. Gong, L. Jiu, J. Bai, M. Warzecha, P. R. Edwards, T. Wang, and R. W. Martin, “Cathodoluminescence studies of chevron features in semi-polar (11-22) InGaN/GaN multiple quantum well structures,” Journal of Applied Physics, 2018.
    [BibTeX] [Abstract] [Download PDF]

    Epitaxial overgrowth of semi-polar III-nitride layers and devices often leads to arrowhead-shaped surface features, referred to as chevrons. We report on a study into the optical, structural and electrical properties of these features occurring in two very different semi-polar structures, a blue-emitting multiple quantum well (MQW) structure and an amber-emitting light-emitting diode (LED). Cathodoluminescence (CL) hyperspectral imaging has highlighted shifts in their emission energy, occurring in the region of the chevron. These variations are due to different semi-polar planes introduced in the chevron arms resulting in a lack of uniformity in the InN incorporation across samples, and the disruption of the structure which could cause a narrowing of the QWs in this region. Atomic force microscopy has revealed that chevrons can penetrate over 150 nm into the sample, and quench light emission from the active layers. The dominance of non-radiative recombination in the chevron region was exposed by simultaneous measurement of CL and the electron beam-induced current (EBIC). Overall these results provide an overview of the nature and impact of chevrons on the luminescence of semi-polar devices.

    @article{strathprints63662,
    month = {April},
    title = {Cathodoluminescence studies of chevron features in semi-polar (11-22) InGaN/GaN multiple quantum well structures},
    author = {C. Brasser and J. Bruckbauer and Y.P. Gong and L. Jiu and J. Bai and M. Warzecha and P. R. Edwards and T. Wang and R. W. Martin},
    year = {2018},
    note = {The following article has been accepted by Journal of Applied Physics. After it is published, it will be found at https://aip.scitation.org/journal/jap/.},
    journal = {Journal of Applied Physics},
    keywords = {semi-polar structures, cathodoluminescence, Physics, Physics and Astronomy(all)},
    url = {https://strathprints.strath.ac.uk/63662/},
    abstract = {Epitaxial overgrowth of semi-polar III-nitride layers and devices often leads to arrowhead-shaped surface features, referred to as chevrons. We report on a study into the optical, structural and electrical properties of these features occurring in two very different semi-polar structures, a blue-emitting multiple quantum well (MQW) structure and an amber-emitting light-emitting diode (LED). Cathodoluminescence (CL) hyperspectral imaging has highlighted shifts in their emission energy, occurring in the region of the chevron. These variations are due to different semi-polar planes introduced in the chevron arms resulting in a lack of uniformity in the InN incorporation across samples, and the disruption of the structure which could cause a narrowing of the QWs in this region. Atomic force microscopy has revealed that chevrons can penetrate over 150 nm into the sample, and quench light emission from the active layers. The dominance of non-radiative recombination in the chevron region was exposed by simultaneous measurement of CL and the electron beam-induced current (EBIC). Overall these results provide an overview of the nature and impact of chevrons on the luminescence of semi-polar devices.}
    }

  • E. Pascal, S. Singh, P. G. Callahan, B. Hourahine, C. Trager-Cowan, and M. D. Graef, “Energy-weighted dynamical scattering simulations of electron diffraction modalites in the scanning electron microscope,” Ultramicroscopy, vol. 187, pp. 98-106, 2018.
    [BibTeX] [Abstract] [Download PDF]

    Transmission Kikuchi diffraction (TKD) has been gaining momentum as a high resolution alternative to electron back-scattered diffraction (EBSD), adding to the existing electron diffraction modalities in the scanning electron microscope (SEM). The image simulation of any of these measurement techniques requires an energy dependent diffraction model for which, in turn, knowledge of electron energies and diffraction distances distributions is required. We identify the sample-detector geometry and the effect of inelastic events on the diffracting electron beam as the important factors to be considered when predicting these distributions. However, tractable models taking into account inelastic scattering explicitly are lacking. In this study, we expand the Monte Carlo (MC) energy-weighting dynamical simulations models used for EBSD and ECP to the TKD case. We show that the foil thickness in TKD can be used as a means of energy filtering and compare band sharpness in the different modalities. The current model is shown to correctly predict TKD patterns and, through the dictionary indexing approach, to produce higher quality indexed TKD maps than conventional Hough transform approach, especially close to grain boundaries.

    @Article{strathprints62987,
    author = {Elena Pascal and Saranch Singh and Patrick G. Callahan and Ben Hourahine and Carol Trager-Cowan and Marc De Graef},
    title = {Energy-weighted dynamical scattering simulations of electron diffraction modalites in the scanning electron microscope},
    journal = {Ultramicroscopy},
    year = {2018},
    volume = {187},
    pages = {98-106},
    month = {January},
    abstract = {Transmission Kikuchi diffraction (TKD) has been gaining momentum as a high resolution alternative to electron back-scattered diffraction (EBSD), adding to the existing electron diffraction modalities in the scanning electron microscope (SEM). The image simulation of any of these measurement techniques requires an energy dependent diffraction model for which, in turn, knowledge of electron energies and diffraction distances distributions is required. We identify the sample-detector geometry and the effect of inelastic events on the diffracting electron beam as the important factors to be considered when predicting these distributions. However, tractable models taking into account inelastic scattering explicitly are lacking. In this study, we expand the Monte Carlo (MC) energy-weighting dynamical simulations models used for EBSD and ECP to the TKD case. We show that the foil thickness in TKD can be used as a means of energy filtering and compare band sharpness in the different modalities. The current model is shown to correctly predict TKD patterns and, through the dictionary indexing approach, to produce higher quality indexed TKD maps than conventional Hough transform approach, especially close to grain boundaries.},
    keywords = {Transmission Kikuchi diffraction, TKD, electron back-scattered diffraction, EBSD, scanning electron microscopes, SEM, electrons, foil thickness, energy filtering, dynamical simulations, Monte Carlo, Plasma physics. Ionized gases, Instrumentation, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials},
    url = {https://strathprints.strath.ac.uk/62987/}
    }

  • K. P. Mingard, M. Stewart, M. G. Gee, S. Vespucci, and C. Trager-Cowan, “Practical application of direct electron detectors to EBSD mapping in 2D and 3D,” Ultramicroscopy, vol. 184, iss. Part A, pp. 242-251, 2018.
    [BibTeX] [Abstract] [Download PDF]

    The use of a direct electron detector for the simple acquisition of 2D electron backscatter diffraction (EBSD) maps and 3D EBSD datasets with a static sample geometry has been demonstrated in a focused ion beam scanning electron microscope. The small size and flexible connection of the Medipix direct electron detector enabled the mounting of sample and detector on the same stage at the short working distance required for the FIB. Comparison of 3D EBSD datasets acquired by this means and with conventional phosphor based EBSD detectors requiring sample movement showed that the former method with a static sample gave improved slice registration. However, for this sample detector configuration, significant heating by the detector caused sample drift. This drift and ion beam reheating both necessitated the use of fiducial marks to maintain stability during data acquisition.

    @article{strathprints62078,
    volume = {184},
    number = {Part A},
    month = {January},
    author = {K.P. Mingard and M. Stewart and M.G. Gee and S. Vespucci and C. Trager-Cowan},
    title = {Practical application of direct electron detectors to EBSD mapping in 2D and 3D},
    journal = {Ultramicroscopy},
    pages = {242--251},
    year = {2018},
    keywords = {EBSD, direct electron detector, medipix, 3D EBSD, SEM image drift, focused ion beam, Optics. Light, Instrumentation, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials},
    url = {https://strathprints.strath.ac.uk/62078/},
    abstract = {The use of a direct electron detector for the simple acquisition of 2D electron backscatter diffraction (EBSD) maps and 3D EBSD datasets with a static sample geometry has been demonstrated in a focused ion beam scanning electron microscope. The small size and flexible connection of the Medipix direct electron detector enabled the mounting of sample and detector on the same stage at the short working distance required for the FIB. Comparison of 3D EBSD datasets acquired by this means and with conventional phosphor based EBSD detectors requiring sample movement showed that the former method with a static sample gave improved slice registration. However, for this sample detector configuration, significant heating by the detector caused sample drift. This drift and ion beam reheating both necessitated the use of fiducial marks to maintain stability during data acquisition.}
    }