• S. Walde, S. Hagedorn, P. -M. Coulon, A. Mogilatenko, C. Netzel, J. Weinrich, N. Susilo, E. Ziffer, L. Matiwe, C. Hartmann, G. Kusch, A. Alasmari, G. Naresh-Kumar, C. Trager-Cowan, T. Wernicke, T. Straubinger, M. Bickermann, R. W. Martin, P. A. Shields, M. Kneissl, and M. Weyers, “AlN overgrowth of nano-pillar-patterned sapphire with different offcut angle by metalorganic vapor phase epitaxy,” Journal of Crystal Growth, vol. 531, p. 125343, 2020.
    [BibTeX] [Abstract] [Download PDF]

    We present overgrowth of nano-patterned sapphire with different offcut angles by metalorganic vapor phase epitaxy. Hexagonal arrays of nano-pillars were prepared via Displacement Talbot Lithography and dry-etching. 6.6 µm crack-free and fully coalesced AlN was grown on such substrates. Extended defect analysis comparing X-ray diffraction, electron channeling contrast imaging and selective defect etching revealed a threading dislocation density of about 10⁹ cm⁻². However, for c-plane sapphire offcut of 0.2° towards m direction the AlN surface shows step bunches with a height of 10 nm. The detrimental impact of these step bunches on subsequently grown AlGaN multi-quantum-wells is investigated by cathodoluminescence and transmission electron microscopy. By reducing the sapphire offcut to 0.1° the formation of step bunches is successfully suppressed. On top of such a sample an AlGaN-based UVC LED heterostructure is realized emitting at 265 nm and showing an emission power of 0.81 mW at 20 mA (corresponds to an external quantum efficiency of 0.86 %).

    @Article{strathprints70583,
    author = {S. Walde and S. Hagedorn and P.-M. Coulon and A. Mogilatenko and C. Netzel and J. Weinrich and N. Susilo and E. Ziffer and L. Matiwe and C. Hartmann and G. Kusch and A. Alasmari and G. Naresh-Kumar and C. Trager-Cowan and T. Wernicke and T. Straubinger and M. Bickermann and R. W. Martin and P. A. Shields and M. Kneissl and M. Weyers},
    journal = {Journal of Crystal Growth},
    title = {{AlN} overgrowth of nano-pillar-patterned sapphire with different offcut angle by metalorganic vapor phase epitaxy},
    year = {2020},
    month = {November},
    pages = {125343},
    volume = {531},
    abstract = {We present overgrowth of nano-patterned sapphire with different offcut angles by metalorganic vapor phase epitaxy. Hexagonal arrays of nano-pillars were prepared via Displacement Talbot Lithography and dry-etching. 6.6 µm crack-free and fully coalesced AlN was grown on such substrates. Extended defect analysis comparing X-ray diffraction, electron channeling contrast imaging and selective defect etching revealed a threading dislocation density of about 10⁹ cm⁻². However, for c-plane sapphire offcut of 0.2° towards m direction the AlN surface shows step bunches with a height of 10 nm. The detrimental impact of these step bunches on subsequently grown AlGaN multi-quantum-wells is investigated by cathodoluminescence and transmission electron microscopy. By reducing the sapphire offcut to 0.1° the formation of step bunches is successfully suppressed. On top of such a sample an AlGaN-based UVC LED heterostructure is realized emitting at 265 nm and showing an emission power of 0.81 mW at 20 mA (corresponds to an external quantum efficiency of 0.86 %).},
    keywords = {metal organic vapor phase epitaxy, nitrides, sapphire, light emitting diodes, Physics, Materials Chemistry, Condensed Matter Physics},
    url = {https://strathprints.strath.ac.uk/70583/},
    }

  • C. Trager-Cowan, A. Alasmari, W. Avis, J. Bruckbauer, P. R. Edwards, G. Ferenczi, B. Hourahine, A. Kotzai, S. Kraeusel, G. Kusch, R. W. Martin, R. McDermott, N. Gunasekar, M. Nouf-Allehiani, E. Pascal, D. Thomson, S. Vespucci, M. D. Smith, P. J. Parbrook, J. Enslin, F. Mehnke, C. Kuhn, T. Wernicke, M. Kneissl, S. Hagedorn, A. Knauer, S. Walde, M. Weyers, P. Coulon, P. Shields, J. Bai, Y. Gong, L. Jiu, Y. Zhang, R. Smith, T. Wang, and A. Winkelmann, “Structural and luminescence imaging and characterisation of semiconductors in the scanning electron microscope,” Semiconductor Science and Technology, vol. 35, p. 54001, 2020.
    [BibTeX] [Abstract] [Download PDF]

    The scanning electron microscopy techniques of electron backscatter diffraction (EBSD), electron channelling contrast imaging (ECCI) and hyperspectral cathodoluminescence imaging (CL) provide complementary information on the structural and luminescence properties of materials rapidly and non-destructively, with a spatial resolution of tens of nanometres. EBSD provides crystal orientation, crystal phase and strain analysis, whilst ECCI is used to determine the planar distribution of extended defects over a large area of a given sample. CL reveals the influence of crystal structure, composition and strain on intrinsic luminescence and/or reveals defect-related luminescence. Dark features are also observed in CL images where carrier recombination at defects is non-radiative. The combination of these techniques is a powerful approach to clarifying the role of crystallography and extended defects on a materials’ light emission properties. Here we describe the EBSD, ECCI and CL techniques and illustrate their use for investigating the structural and light emitting properties of UV-emitting nitride semiconductor structures. We discuss our investigations of the type, density and distribution of defects in GaN, AlN and AlGaN thin films and also discuss the determination of the polarity of GaN nanowires.

    @Article{strathprints71512,
    author = {Carol Trager-Cowan and Aeshah Alasmari and William Avis and Jochen Bruckbauer and Paul R. Edwards and Gergely Ferenczi and Benjamin Hourahine and Almpes Kotzai and Simon Kraeusel and Gunnar Kusch and Robert W. Martin and Ryan McDermott and Naresh Gunasekar and M. Nouf-Allehiani and Elena Pascal and David Thomson and Stefano Vespucci and Matthew David Smith and Peter J. Parbrook and Johannes Enslin and Frank Mehnke and Christian Kuhn and Tim Wernicke and Michael Kneissl and Sylvia Hagedorn and Arne Knauer and Sebastian Walde and Markus Weyers and Pierre-Marie Coulon and Philip Shields and J. Bai and Y. Gong and Ling Jiu and Y. Zhang and Richard Smith and Tao Wang and Aimo Winkelmann},
    journal = {Semiconductor Science and Technology},
    title = {Structural and luminescence imaging and characterisation of semiconductors in the scanning electron microscope},
    year = {2020},
    month = {February},
    pages = {054001},
    volume = {35},
    abstract = {The scanning electron microscopy techniques of electron backscatter diffraction (EBSD), electron channelling contrast imaging (ECCI) and hyperspectral cathodoluminescence imaging (CL) provide complementary information on the structural and luminescence properties of materials rapidly and non-destructively, with a spatial resolution of tens of nanometres. EBSD provides crystal orientation, crystal phase and strain analysis, whilst ECCI is used to determine the planar distribution of extended defects over a large area of a given sample. CL reveals the influence of crystal structure, composition and strain on intrinsic luminescence and/or reveals defect-related luminescence. Dark features are also observed in CL images where carrier recombination at defects is non-radiative. The combination of these techniques is a powerful approach to clarifying the role of crystallography and extended defects on a materials' light emission properties. Here we describe the EBSD, ECCI and CL techniques and illustrate their use for investigating the structural and light emitting properties of UV-emitting nitride semiconductor structures. We discuss our investigations of the type, density and distribution of defects in GaN, AlN and AlGaN thin films and also discuss the determination of the polarity of GaN nanowires.},
    keywords = {EBSD, nitride, scanning electron microscopy, Physics, Electronic, Optical and Magnetic Materials, Electrical and Electronic Engineering, Condensed Matter Physics},
    url = {https://strathprints.strath.ac.uk/71512/},
    }

  • C. Trager-Cowan, A. Alasmari, W. Avis, J. Bruckbauer, P. R. Edwards, B. Hourahine, S. Kraeusel, G. Kusch, R. Johnston, G. Naresh-Kumar, R. W. Martin, M. Nouf-Allehiani, E. Pascal, L. Spasevski, D. Thomson, S. Vespucci, P. J. Parbrook, M. D. Smith, J. Enslin, F. Mehnke, M. Kneissl, C. Kuhn, T. Wernicke, S. Hagedorn, S. Walde, M. Weyers, P. -M. Coulon, P. A. Shields, Y. Zhang, L. Jiu, Y. P. Gong, R. M. Smith, T. Wang, and A. Winkelmann, “The scanning electron microscope as a flexible tool for investigating the properties of UV-emitting nitride semiconductor thin films,” Photonics Research, vol. 7, iss. 11, p. B73–B82, 2019.
    [BibTeX] [Abstract] [Download PDF]

    In this article we describe the scanning electron microscopy techniques of electron backscatter diffraction (EBSD), electron channelling contrast imaging (ECCI), wavelength dispersive X-ray spectroscopy (WDX) and cathodoluminescence (CL) hyperspectral imaging. We present our recent results on the use of these non-destructive techniques to obtain information on the topography, crystal misorientation, defect distributions, composition, doping and light emission from a range of UV emitting nitride semiconductor structures. We aim to illustrate the developing capability of each of these techniques for understanding the properties of UV emitting nitride semiconductors, and the benefits were appropriate, in combining the techniques.

    @Article{strathprints69913,
    author = {C. Trager-Cowan and A. Alasmari and W. Avis and Jochen Bruckbauer and P. R. Edwards and B. Hourahine and S. Kraeusel and G. Kusch and R. Johnston and G. Naresh-Kumar and R. W. Martin and M. Nouf-Allehiani and E. Pascal and L. Spasevski and D. Thomson and S. Vespucci and P. J. Parbrook and M. D. Smith and J. Enslin and F. Mehnke and M. Kneissl and C. Kuhn and T. Wernicke and S. Hagedorn and S. Walde and M. Weyers and P.-M. Coulon and P. A. Shields and Y. Zhang and L. Jiu and Y. P. Gong and R. M. Smith and T. Wang and A. Winkelmann},
    title = {The scanning electron microscope as a flexible tool for investigating the properties of {UV}-emitting nitride semiconductor thin films},
    journal = {Photonics Research},
    year = {2019},
    volume = {7},
    number = {11},
    pages = {B73--B82},
    month = {September},
    abstract = {In this article we describe the scanning electron microscopy techniques of electron backscatter diffraction (EBSD), electron channelling contrast imaging (ECCI), wavelength dispersive X-ray spectroscopy (WDX) and cathodoluminescence (CL) hyperspectral imaging. We present our recent results on the use of these non-destructive techniques to obtain information on the topography, crystal misorientation, defect distributions, composition, doping and light emission from a range of UV emitting nitride semiconductor structures. We aim to illustrate the developing capability of each of these techniques for understanding the properties of UV emitting nitride semiconductors, and the benefits were appropriate, in combining the techniques.},
    keywords = {scanning electron microscopy, electron backscatter diffraction, non-destructive techniques, UV emitting nitride semiconductors, Physics, Atomic and Molecular Physics, and Optics},
    url = {https://strathprints.strath.ac.uk/69913/},
    }

  • J. Enslin, T. Wernicke, A. Lobanova, G. Kusch, L. Spasevski, T. Teke, B. Belde, R. W. Martin, R. Talalaev, and M. Kneissl, “Indium incorporation in quaternary Inx Aly Ga1-x-y N for UVB-LEDs,” Japanese Journal of Applied Physics, vol. 58, iss. SC, p. SC1004, 2019.
    [BibTeX] [Abstract] [Download PDF]

    Consistent studies of the quaternary composition are rare as it is impossible to fully determine the quaternary composition by X-ray diffraction or deduce it from that of ternary alloys. In this paper we determined the quaternary composition by wavelength dispersive X-ray spectroscopy of Inx Aly layers grown by metal organic vapor phase epitaxy. Further insights explaining the peculiarities of Inx Aly Ga1-x-yN growth in a showerhead reactor were gained by simulations of the precursor decomposition, gas phase adduct formation and indium incorporation including desorption. The measurements and simulations agree very well showing that the indium incorporation in a range from 0\% to 2\% is limited by desorption which is enhanced by the compressive strain to the relaxed Al0.5Ga0.5N buffer layer as well as indium incorporation into AlN particles forming in the gas phase. Utilizing Inx Aly Ga1-x-yN layers containing 2\% of indium for multiple quantum wells (MQWs), it was possible to show an almost five times higher photoluminescence intensity of InAlGaN MQWs in comparison to AlGaN MQWs.

    @Article{strathprints71494,
    author = {Johannes Enslin and Tim Wernicke and Anna Lobanova and Gunnar Kusch and Lucia Spasevski and Tolga Teke and Bettina Belde and Robert W. Martin and Roman Talalaev and Michael Kneissl},
    title = {Indium incorporation in quaternary Inx Aly Ga1-x-y N for UVB-LEDs},
    journal = {Japanese Journal of Applied Physics},
    year = {2019},
    volume = {58},
    number = {SC},
    pages = {SC1004},
    month = {April},
    abstract = {Consistent studies of the quaternary composition are rare as it is impossible to fully determine the quaternary composition by X-ray diffraction or deduce it from that of ternary alloys. In this paper we determined the quaternary composition by wavelength dispersive X-ray spectroscopy of Inx Aly layers grown by metal organic vapor phase epitaxy. Further insights explaining the peculiarities of Inx Aly Ga1-x-yN growth in a showerhead reactor were gained by simulations of the precursor decomposition, gas phase adduct formation and indium incorporation including desorption. The measurements and simulations agree very well showing that the indium incorporation in a range from 0\% to 2\% is limited by desorption which is enhanced by the compressive strain to the relaxed Al0.5Ga0.5N buffer layer as well as indium incorporation into AlN particles forming in the gas phase. Utilizing Inx Aly Ga1-x-yN layers containing 2\% of indium for multiple quantum wells (MQWs), it was possible to show an almost five times higher photoluminescence intensity of InAlGaN MQWs in comparison to AlGaN MQWs.},
    keywords = {quaternary composition, X-ray spectroscopy, X-ray diffraction, UVB, ultraviolet light, light emitting diodes, LEDs, Physics, Physics and Astronomy(all)},
    url = {https://strathprints.strath.ac.uk/71494/},
    }

  • G. Kusch, J. Enslin, L. Spasevski, T. Teke, T. Wernicke, P. R. Edwards, M. Kneissl, and R. W. Martin, “Influence of InN and AlN concentration on the compositional inhomogeneity and formation of InN-rich regions in InxAlyGa1-x-yN,” Japanese Journal of Applied Physics, vol. 58, p. SCCB18, 2019.
    [BibTeX] [Abstract] [Download PDF]

    The application of quaternary InxAlyGa1-x-yN active regions is a promising path towards high efficiency UVB-LEDs. For the utilisation of InxAlyGa1-x-yN, detailed knowledge of the interplay between growth parameters, adatom incorporation, optical and structural properties is crucial. We investigated the influence of the TMAl and TMIn flux on the composition and luminescence properties of InxAlyGa1-x-yN layers by multi-mode scanning electron microscopy. We found that varying the molar TMIn flow from 0 to 17.3 µmol/min led to an InN concentration between 0% and 3.2% and an emission energy between 4.17 eV and 3.75 eV. The variation of the molar TMAl flow from 3.5 to 35.4 µmol/min resulted in a AlN composition between 7.8% and 30.7% with an emission energy variation between 3.6 eV and 4.1 eV. Cathodoluminescence hyperspectral imaging provided evidence for the formation of nanoscale InN-rich regions. Analysing the emission properties of these InN-rich regions showed that their emission energy is inhomogeneous and varies by ~150 meV. We provide evidence that the formation of these InN-rich regions is highly dependent on the AlN and InN composition of the layer and that their formation will strongly affect the performance of InxAlyGa1-x-yN LEDs.

    @Article{strathprints67321,
    author = {Gunnar Kusch and Johannes Enslin and Lucia Spasevski and Tolga Teke and Tim Wernicke and Paul R. Edwards and Michael Kneissl and Robert W. Martin},
    title = {Influence of InN and AlN concentration on the compositional inhomogeneity and formation of InN-rich regions in InxAlyGa1-x-yN},
    journal = {Japanese Journal of Applied Physics},
    year = {2019},
    volume = {58},
    pages = {SCCB18},
    month = {March},
    abstract = {The application of quaternary InxAlyGa1-x-yN active regions is a promising path towards high efficiency UVB-LEDs. For the utilisation of InxAlyGa1-x-yN, detailed knowledge of the interplay between growth parameters, adatom incorporation, optical and structural properties is crucial. We investigated the influence of the TMAl and TMIn flux on the composition and luminescence properties of InxAlyGa1-x-yN layers by multi-mode scanning electron microscopy. We found that varying the molar TMIn flow from 0 to 17.3 µmol/min led to an InN concentration between 0% and 3.2% and an emission energy between 4.17 eV and 3.75 eV. The variation of the molar TMAl flow from 3.5 to 35.4 µmol/min resulted in a AlN composition between 7.8% and 30.7% with an emission energy variation between 3.6 eV and 4.1 eV. Cathodoluminescence hyperspectral imaging provided evidence for the formation of nanoscale InN-rich regions. Analysing the emission properties of these InN-rich regions showed that their emission energy is inhomogeneous and varies by ~150 meV. We provide evidence that the formation of these InN-rich regions is highly dependent on the AlN and InN composition of the layer and that their formation will strongly affect the performance of InxAlyGa1-x-yN LEDs.},
    keywords = {high efficiency UVB-LEDs, composition, luminescence, cathodoluminescence hyperspectral imaging, Physics, Physics and Astronomy(all)},
    url = {https://strathprints.strath.ac.uk/67321/}
    }

  • G. Kusch, F. Mehnke, J. Enslin, P. R. Edwards, T. Wernicke, M. Kneissl, and R. W. Martin, “Analysis of doping concentration and composition in wide bandgap AlGaN:Si by wavelength dispersive X-ray spectroscopy,” Semiconductor Science and Technology, vol. 32, iss. 3, p. 35020, 2017.
    [BibTeX] [Abstract] [Download PDF]

    Detailed knowledge of the dopant concentration and composition of wide band gap AlxGa1?xN layers is of crucial importance for the fabrication of ultra violet (UV) light emitting diodes (LEDs). This paper demonstrates the capabilities of wavelength dispersive X-ray (WDX) spectroscopy in accurately determining these parameters and compares the results with those from high resolution X-ray diffraction (HR-XRD) and secondary ion mass spectrometry (SIMS). WDX spectroscopy has been carried out on different silicon-doped wide bandgap AlxGa1?xN samples (x between 0.80 and 1). This study found a linear increase in the Si concentration with the SiH4/group-III ratio, measuring Si concentrations between 3{$\times$}1018 cm?3 and 2.8{$\times$}1019 cm?3, while no direct correlation between the AlN composition and the Si incorporation ratio was found. Comparison between the composition obtained by WDX and by HR-XRD showed very good agreement in the range investigated, while comparison of the donor concentration between WDX and SIMS found only partial agreement, which we attribute to a number of effects.

    @Article{strathprints59282,
    author = {Gunnar Kusch and Frank Mehnke and Johannes Enslin and Paul R Edwards and Tim Wernicke and Michael Kneissl and Robert W Martin},
    title = {Analysis of doping concentration and composition in wide bandgap {AlGaN:Si} by wavelength dispersive {X}-ray spectroscopy},
    journal = {Semiconductor Science and Technology},
    year = {2017},
    volume = {32},
    number = {3},
    pages = {035020},
    month = {February},
    abstract = {Detailed knowledge of the dopant concentration and composition of wide band gap AlxGa1?xN layers is of crucial importance for the fabrication of ultra violet (UV) light emitting diodes (LEDs). This paper demonstrates the capabilities of wavelength dispersive X-ray (WDX) spectroscopy in accurately determining these parameters and compares the results with those from high resolution X-ray diffraction (HR-XRD) and secondary ion mass spectrometry (SIMS). WDX spectroscopy has been carried out on different silicon-doped wide bandgap AlxGa1?xN samples (x between 0.80 and 1). This study found a linear increase in the Si concentration with the SiH4/group-III ratio, measuring Si concentrations between 3{$\times$}1018 cm?3 and 2.8{$\times$}1019 cm?3, while no direct correlation between the AlN composition and the Si incorporation ratio was found. Comparison between the composition obtained by WDX and by HR-XRD showed very good agreement in the range investigated, while comparison of the donor concentration between WDX and SIMS found only partial agreement, which we attribute to a number of effects.},
    keywords = {dopant concentration, ultra violet light emitting diodes, wavelength dispersive X-ray spectroscopy, high resolution X-ray diffraction, doping concentrations, semiconductors, dopant composition, Physics, Physics and Astronomy(all)},
    url = {http://strathprints.strath.ac.uk/59282/}
    }

  • G. Kusch, M. Nouf-Allehiani, F. Mehnke, C. Kuhn, P. R. Edwards, T. Wernicke, A. Knauer, V. Kueller, G. Naresh-Kumar, M. Weyers, M. Kneissl, C. Trager-Cowan, and R. W. Martin, “Spatial clustering of defect luminescence centers in Si-doped low resistivity Al₀.₈₂Ga₀.₁₈N,” Applied Physics Letters, vol. 107, iss. 7, p. 72103, 2015.
    [BibTeX] [Abstract] [Download PDF]

    A series of Si-doped AlN-rich AlGaN layers with low resistivities was characterized by a combination of nanoscale imaging techniques. Utilizing the capability of scanning electron microscopy to reliably investigate the same sample area with different techniques, it was possible to determine the effect of doping concentration, defect distribution, and morphology on the luminescence properties of these layers. Cathodoluminescence shows that the dominant defect luminescence depends on the Si-doping concentration. For lower doped samples, the most intense peak was centered between 3.36 eV and 3.39 eV, while an additional, stronger peak appears at 3 eV for the highest doped sample. These peaks were attributed to the (VIII-ON)2? complex and the VIII3? vacancy, respectively. Multimode imaging using cathodoluminescence, secondary electrons, electron channeling contrast, and atomic force microscopy demonstrates that the luminescence intensity of these peaks is not homogeneously distributed but shows a strong dependence on the topography and on the distribution of screw dislocations.

    @Article{strathprints54134,
    author = {Gunnar Kusch and M. Nouf-Allehiani and Frank Mehnke and Christian Kuhn and Paul R. Edwards and Tim Wernicke and Arne Knauer and Viola Kueller and G. Naresh-Kumar and Markus Weyers and Michael Kneissl and Carol Trager-Cowan and Robert W. Martin},
    title = {Spatial clustering of defect luminescence centers in {Si}-doped low resistivity {Al₀.₈₂Ga₀.₁₈N}},
    journal = {Applied Physics Letters},
    year = {2015},
    volume = {107},
    number = {7},
    pages = {072103},
    month = {August},
    abstract = {A series of Si-doped AlN-rich AlGaN layers with low resistivities was characterized by a combination of nanoscale imaging techniques. Utilizing the capability of scanning electron microscopy to reliably investigate the same sample area with different techniques, it was possible to determine the effect of doping concentration, defect distribution, and morphology on the luminescence properties of these layers. Cathodoluminescence shows that the dominant defect luminescence depends on the Si-doping concentration. For lower doped samples, the most intense peak was centered between 3.36 eV and 3.39 eV, while an additional, stronger peak appears at 3 eV for the highest doped sample. These peaks were attributed to the (VIII-ON)2? complex and the VIII3? vacancy, respectively. Multimode imaging using cathodoluminescence, secondary electrons, electron channeling contrast, and atomic force microscopy demonstrates that the luminescence intensity of these peaks is not homogeneously distributed but shows a strong dependence on the topography and on the distribution of screw dislocations.},
    keywords = {nanoscale imaging, cathodoluminescence, multimode imaging, Physics, Physics and Astronomy (miscellaneous)},
    url = {http://strathprints.strath.ac.uk/54134/}
    }

  • G. Naresh-Kumar, A. Vilalta-Clemente, S. Pandey, D. Skuridina, H. Behmenburg, P. Gamarra, G. Patriarche, I. Vickridge, M. A. di Forte-Poisson, P. Vogt, M. Kneissl, M. Morales, P. Ruterana, A. Cavallini, D. Cavalcoli, C. Giesen, M. Heuken, and C. Trager-Cowan, “Multicharacterization approach for studying InAl(Ga)N/Al(Ga)N/GaN heterostructures for high electron mobility transistors,” AIP Advances, vol. 4, iss. 12, p. 127101, 2014.
    [BibTeX] [Abstract] [Download PDF]

    We report on our multi?pronged approach to understand the structural and electrical properties of an InAl(Ga)N(33nm barrier)/Al(Ga)N(1nm interlayer)/GaN(3{\ensuremath{\mu}}m)/AlN(100nm)/Al2O3 high electron mobility transistor (HEMT) heterostructure grown by metal organic vapor phase epitaxy (MOVPE). In particular we reveal and discuss the role of unintentional Ga incorporation in the barrier and also in the interlayer. The observation of unintentional Ga incorporation by using energy dispersive X?ray spectroscopy analysis in a scanning transmission electron microscope is supported with results obtained for samples with a range of AlN interlayer thicknesses grown under both the showerhead as well as the horizontal type MOVPE reactors. Poisson?Schrödinger simulations show that for high Ga incorporation in the Al(Ga)N interlayer, an additional triangular well with very small depth may be exhibited in parallel to the main 2?DEG channel. The presence of this additional channel may cause parasitic conduction and severe issues in device characteristics and processing. Producing a HEMT structure with InAlGaN as the barrier and AlGaN as the interlayer with appropriate alloy composition may be a possible route to optimization, as it might be difficult to avoid Ga incorporation while continuously depositing the layers using the MOVPE growth method. Our present work shows the necessity of a multicharacterization approach to correlate structural and electrical properties to understand device structures and their performance.

    @Article{strathprints50638,
    author = {G. Naresh-Kumar and A. Vilalta-Clemente and S. Pandey and D. Skuridina and H. Behmenburg and P. Gamarra and G. Patriarche and I. Vickridge and M. A. di Forte-Poisson and P. Vogt and M. Kneissl and M. Morales and P. Ruterana and A. Cavallini and D. Cavalcoli and C. Giesen and M. Heuken and C. Trager-Cowan},
    title = {Multicharacterization approach for studying InAl(Ga)N/Al(Ga)N/GaN heterostructures for high electron mobility transistors},
    journal = {AIP Advances},
    year = {2014},
    volume = {4},
    number = {12},
    pages = {127101},
    month = {December},
    abstract = {We report on our multi?pronged approach to understand the structural and electrical properties of an InAl(Ga)N(33nm barrier)/Al(Ga)N(1nm interlayer)/GaN(3{\ensuremath{\mu}}m)/AlN(100nm)/Al2O3 high electron mobility transistor (HEMT) heterostructure grown by metal organic vapor phase epitaxy (MOVPE). In particular we reveal and discuss the role of unintentional Ga incorporation in the barrier and also in the interlayer. The observation of unintentional Ga incorporation by using energy dispersive X?ray spectroscopy analysis in a scanning transmission electron microscope is supported with results obtained for samples with a range of AlN interlayer thicknesses grown under both the showerhead as well as the horizontal type MOVPE reactors. Poisson?Schr{\"o}dinger simulations show that for high Ga incorporation in the Al(Ga)N interlayer, an additional triangular well with very small depth may be exhibited in parallel to the main 2?DEG channel. The presence of this additional channel may cause parasitic conduction and severe issues in device characteristics and processing. Producing a HEMT structure with InAlGaN as the barrier and AlGaN as the interlayer with appropriate alloy composition may be a possible route to optimization, as it might be difficult to avoid Ga incorporation while continuously depositing the layers using the MOVPE growth method. Our present work shows the necessity of a multicharacterization approach to correlate structural and electrical properties to understand device structures and their performance.},
    keywords = {Ga incorporation, III-V semiconductors, Rutherford backscattering, Physics, Electronic, Optical and Magnetic Materials, Physics and Astronomy (miscellaneous)},
    url = {http://strathprints.strath.ac.uk/50638/}
    }