@article{szymanski_wang_kaess_kirste_mita_reddy_sitar_collazo_2022, title={Systematic oxygen impurity reduction in smooth N-polar GaN by chemical potential control}, volume={37}, ISSN={["1361-6641"]}, DOI={10.1088/1361-6641/ac3638}, abstractNote={Abstract}, number={1}, journal={SEMICONDUCTOR SCIENCE AND TECHNOLOGY}, author={Szymanski, Dennis and Wang, Ke and Kaess, Felix and Kirste, Ronny and Mita, Seiji and Reddy, Pramod and Sitar, Zlatko and Collazo, Ramon}, year={2022}, month={Jan} }
 @article{washiyama_reddy_kaess_kirste_mita_collazo_sitar_2018, title={A thermodynamic supersaturation model for the growth of aluminum gallium nitride by metalorganic chemical vapor deposition}, volume={124}, ISSN={["1089-7550"]}, url={https://doi.org/10.1063/1.5045058}, DOI={10.1063/1.5045058}, abstractNote={A thermodynamic supersaturation model for growth of AlGaN by metalorganic chemical vapor deposition was developed for experimentally accessible growth parameters. The derived non-linear relationships enabled us to estimate Ga and Al supersaturation during AlGaN growth for given growth conditions. Calculations revealed that the GaN phase was close to chemical equilibrium, while the Al supersaturation was as high as 1010 for typical growth conditions. Such a disparity in the supersaturation of reaction species plays a significant role in the stability of the growth of the resulting ternary alloy. The agreement between experiment and simulation suggests that the parasitic gas phase reactions between trimethylaluminum and NH3 were not significant at low NH3 flow rates/partial pressures, indicating that, under these conditions, the AlGaN growth was thermodynamically limited.}, number={11}, journal={JOURNAL OF APPLIED PHYSICS}, author={Washiyama, Shun and Reddy, Pramod and Kaess, Felix and Kirste, Ronny and Mita, Seiji and Collazo, Ramon and Sitar, Zlatko}, year={2018}, month={Sep} }
 @article{reddy_washiyama_mecouch_hernandez-balderrama_kaess_breckenridge_sarkar_haidet_franke_kohn_et al._2018, title={Plasma enhanced chemical vapor deposition of SiO2 and SiNx on AlGaN: Band offsets and interface studies as a function of Al composition}, volume={36}, ISSN={["1520-8559"]}, DOI={10.1116/1.5050501}, abstractNote={In this work, the authors characterized the interface of plasma enhanced chemical vapor deposition (PECVD) dielectrics, SiO2 and SiNx with AlGaN as a function of Al composition. SiO2 is found to exhibit type I straddled band alignment with positive conduction and valence band offsets for all Al compositions. However, the interface Fermi level is found to be pinned within the bandgap, indicating a significant density of interface states. Hence, SiO2 is found to be suitable for insulating layers or electrical isolation on AlGaN with breakdown fields between 4.5 and 6.5 MV cm−1, but an additional passivating interlayer between SiO2 and AlGaN is necessary for passivation on Al-rich AlGaN. In contrast, Si-rich PECVD SiNx is found to exhibit type II staggered band alignment with positive conduction band offsets and negative valence band offsets for Al compositions <40% and type I straddled band alignment with negative conduction and valence band offsets for Al compositions >40% and is, hence, found to be unsuitable for insulating layers or electrical isolation on Al-rich AlGaN in general. In contrast to passivating stoichiometric LPCVD Si3N4, no evidence for interface state reduction by depositing SiNx on AlGaN is observed.}, number={6}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Reddy, Pramod and Washiyama, Shun and Mecouch, Will and Hernandez-Balderrama, Luis H. and Kaess, Felix and Breckenridge, M. Hayden and Sarkar, Biplab and Haidet, Brian B. and Franke, Alexander and Kohn, Erhard and et al.}, year={2018}, month={Nov} }
 @article{blumenschein_slomski_paskov_kaess_breckenridge_muth_paskova_2018, title={Thermal conductivity of bulk and thin film beta-Ga2O3 measured by the 3 omega technique}, volume={10533}, ISSN={["1996-756X"]}, DOI={10.1117/12.2288267}, abstractNote={Thermal conductivity of undoped and Sn-doped β-Ga2O3 bulk and single-crystalline thin films have been measured by the 3ω technique. The bulk samples were grown by edge-defined film-field growth (EFG) method, while the thin films were grown on c-plane sapphire by pulsed-laser deposition (PLD). All samples were with (-201) surface orientation. Thermal conductivity of bulk samples was calculated along the in-plane and cross-plane crystallographic directions, yielding a maximum value of ~ 29 W/m-K in the [010] direction at room temperature. A slight thermal conductivity decrease was observed in the Sn-doped bulk samples, which was attributed to enhanced phonon-impurity scattering. The differential 3ω method was used for β-Ga2O3 thin film samples due to the small film thickness. Results show that both undoped and Sndoped films have a much lower thermal conductivity than that of the bulk samples, which is consistent with previous reports in the literature showing a linear relationship between thermal conductivity and film thickness. Similarly to bulk samples, Sn-doped thin films have exhibited a thermal conductivity decrease. However, this decrease was found to be much greater in thin film samples, and increased with Sn doping concentration. A correlation between thermal conductivity and defect/dislocation density was made for the undoped thin films.}, journal={OXIDE-BASED MATERIALS AND DEVICES IX}, author={Blumenschein, N. and Slomski, M. and Paskov, P. P. and Kaess, F. and Breckenridge, M. H. and Muth, J. F. and Paskova, T.}, year={2018} }
 @article{sarkar_reddy_kaess_haidet_tweedie_mita_kirste_kohn_collazo_sitar_et al._2017, title={(Invited) Material Considerations for the Development of III-nitride Power Devices}, volume={80}, ISBN={["978-1-62332-476-6"]}, ISSN={["1938-6737"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85033580489&partnerID=MN8TOARS}, DOI={10.1149/08007.0029ecst}, abstractNote={With advancement in growth of native III-nitride substrates, remarkable progress has been made to extend the functionality of GaN based power electronic devices. The low dislocation epitaxial films grown on native substrates outperforms the films grown on foreign substrates. However, several material considerations has to be incorporated in order to exploit the full potential of GaN and AlxGa1-xN (0<x≤1) based power devices. This paper presents a review report on the development of III-nitride power devices grown on foreign and native (GaN and AlN) substrates. Discussion on state-of-the art epitaxial material quality, contact formation and surface treatments films are presented.}, number={7}, journal={GALLIUM NITRIDE AND SILICON CARBIDE POWER TECHNOLOGIES 7}, author={Sarkar, B. and Reddy, Pramod and Kaess, F. and Haidet, B.B. and Tweedie, J. and Mita, S. and Kirste, R. and Kohn, E. and Collazo, R. and Sitar, Z. and et al.}, year={2017}, pages={29–36} }
 @article{reddy_kaess_tweedie_kirste_mita_collazo_sitar_2017, title={Defect quasi Fermi level control-based C-N reduction in GaN: Evidence for the role of minority carriers}, volume={111}, ISSN={["1077-3118"]}, url={https://doi.org/10.1063/1.5000720}, DOI={10.1063/1.5000720}, abstractNote={Compensating point defect reduction in wide bandgap semiconductors is possible by above bandgap illumination based defect quasi Fermi level (dQFL) control. The point defect control technique employs excess minority carriers that influence the dQFL of the compensator, increase the corresponding defect formation energy, and consequently are responsible for point defect reduction. Previous studies on various defects in GaN and AlGaN have shown good agreement with the theoretical model, but no direct evidence for the role of minority carriers was provided. In this work, we provide direct evidence for the role of minority carriers in reducing point defects by studying the predicted increase in work done against defect (CN−1) formation with the decrease in the Fermi level (free carrier concentration) in Si doped GaN at a constant illumination intensity. Comparative defect photoluminescence measurements on illuminated and dark regions of GaN show an excellent quantitative agreement with the theory by exhibiting a greater reduction in yellow luminescence attributed to CN−1 at lower doping, thereby providing conclusive evidence for the role of the minority carriers in Fermi level control-based point defect reduction.}, number={15}, journal={APPLIED PHYSICS LETTERS}, publisher={AIP Publishing}, author={Reddy, Pramod and Kaess, Felix and Tweedie, James and Kirste, Ronny and Mita, Seiji and Collazo, Ramon and Sitar, Zlatko}, year={2017}, month={Oct} }
 @article{reddy_sarkar_kaess_gerhold_kohn_collazo_sitar_2017, title={Defect-free Ni/GaN Schottky barrier behavior with high temperature stability}, volume={110}, ISSN={["1077-3118"]}, url={https://doi.org/10.1063/1.4973762}, DOI={10.1063/1.4973762}, abstractNote={In this work, we report on defect-free homogeneous behavior of Ni Schottky contacts patterned on surface treated n-GaN by photolithography with unity ideality factor, high temperature stability, and low reverse leakage. The barrier height (0.7 eV) and ideality factor (1.02) are found to be independent of temperature, indicating a highly homogeneous contact. The contacts are found to be stable with no significant change in ideality factor or leakage current up to an annealing temperature of 600 °C. Temperature dependence of the reverse leakage current shows no evidence for the existence of surface defects that would provide leakage paths, and the behavior was modeled by ATLAS simulations with an ideal homogeneous barrier of 0.7 eV. Consequently, the forward and reverse bias characteristics are explained by a common set of parameters. The surface treatment after the development and prior to metallization included an acid-based surface treatment. X-ray photoelectron spectroscopy (XPS) studies indicate that the hydroxide-based development process during photolithography changes the nitride surface composition by introducing excess C that degrades the ideality factor and introduces barrier inhomogeneity and high leakage currents. XPS studies further demonstrate that the restoration of a stable, Ga-rich surface, similar to as-grown surface, occurs due to the acid-based surface treatment, which is responsible for the observed unity ideality factor, homogeneous barrier, low leakage current, and high temperature stability.}, number={1}, journal={APPLIED PHYSICS LETTERS}, publisher={AIP Publishing}, author={Reddy, Pramod and Sarkar, Biplab and Kaess, Felix and Gerhold, Michael and Kohn, Erhard and Collazo, Ramon and Sitar, Zlatko}, year={2017}, month={Jan} }
 @article{sarkar_mita_reddy_klump_kaess_tweedie_bryan_bryan_kirste_kohn_et al._2017, title={High free carrier concentration in p-GaN grown on AlN substrates}, volume={111}, ISSN={["1077-3118"]}, url={https://doi.org/10.1063/1.4995239}, DOI={10.1063/1.4995239}, abstractNote={A high free hole concentration in III-nitrides is important for next generation optoelectronic and high power electronic devices. The free hole concentration exceeding 1018 cm−3 and resistivity as low as 0.7 Ω cm are reported for p-GaN layers grown by metalorganic vapor phase epitaxy on single crystal AlN substrates. Temperature dependent Hall measurements confirmed a much lower activation energy, 60–80 mV, for p-GaN grown on AlN as compared to sapphire substrates; the lowering of the activation energy was due to screening of Coulomb potential by free carriers. It is also shown that a higher doping density (more than 5 × 1019 cm−3) can be achieved in p-GaN/AlN without the onset of self-compensation.}, number={3}, journal={APPLIED PHYSICS LETTERS}, publisher={AIP Publishing}, author={Sarkar, Biplab and Mita, Seiji and Reddy, Pramod and Klump, Andrew and Kaess, Felix and Tweedie, James and Bryan, Isaac and Bryan, Zachary and Kirste, Ronny and Kohn, Erhard and et al.}, year={2017}, month={Jul} }
 @article{reddy_washiyama_kaess_kirste_mita_collazo_sitar_2017, title={Point defect reduction in MOCVD (Al)GaN by chemical potential control and a comprehensive model of C incorporation in GaN}, volume={122}, url={https://doi.org/10.1063/1.5002682}, DOI={10.1063/1.5002682}, abstractNote={A theoretical framework that provides a quantitative relationship between point defect formation energies and growth process parameters is presented. It enables systematic point defect reduction by chemical potential control in metalorganic chemical vapor deposition (MOCVD) of III-nitrides. Experimental corroboration is provided by a case study of C incorporation in GaN. The theoretical model is shown to be successful in providing quantitative predictions of CN defect incorporation in GaN as a function of growth parameters and provides valuable insights into boundary phases and other impurity chemical reactions. The metal supersaturation is found to be the primary factor in determining the chemical potential of III/N and consequently incorporation or formation of point defects which involves exchange of III or N atoms with the reservoir. The framework is general and may be extended to other defect systems in (Al)GaN. The utility of equilibrium formalism typically employed in density functional theory in predicting defect incorporation in non-equilibrium and high temperature MOCVD growth is confirmed. Furthermore, the proposed theoretical framework may be used to determine optimal growth conditions to achieve minimum compensation within any given constraints such as growth rate, crystal quality, and other practical system limitations.}, number={24}, journal={Journal of Applied Physics}, publisher={AIP Publishing}, author={Reddy, Pramod and Washiyama, Shun and Kaess, Felix and Kirste, Ronny and Mita, Seiji and Collazo, Ramon and Sitar, Zlatko}, year={2017}, month={Dec}, pages={245702} }
 @article{kaess_mita_xie_reddy_klump_hernandez-balderrama_washiyama_franke_kirste_hoffmann_et al._2016, title={Correlation between mobility collapse and carbon impurities in Si-doped GaN grown by low pressure metalorganic chemical vapor deposition}, volume={120}, ISSN={["1089-7550"]}, url={https://doi.org/10.1063/1.4962017}, DOI={10.1063/1.4962017}, abstractNote={In the low doping range below 1 × 1017 cm−3, carbon was identified as the main defect attributing to the sudden reduction of the electron mobility, the electron mobility collapse, in n-type GaN grown by low pressure metalorganic chemical vapor deposition. Secondary ion mass spectroscopy has been performed in conjunction with C concentration and the thermodynamic Ga supersaturation model. By controlling the ammonia flow rate, the input partial pressure of Ga precursor, and the diluent gas within the Ga supersaturation model, the C concentration in Si-doped GaN was controllable from 6 × 1019 cm−3 to values as low as 2 × 1015 cm−3. It was found that the electron mobility collapsed as a function of free carrier concentration, once the Si concentration closely approached the C concentration. Lowering the C concentration to the order of 1015 cm−3 by optimizing Ga supersaturation achieved controllable free carrier concentrations down to 5 × 1015 cm−3 with a peak electron mobility of 820 cm2/V s without observing the mobility collapse. The highest electron mobility of 1170 cm2/V s was obtained even in metalorganic vapor deposition-grown GaN on sapphire substrates by optimizing growth parameters in terms of Ga supersaturation to reduce the C concentration.}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, publisher={AIP Publishing}, author={Kaess, Felix and Mita, Seiji and Xie, Jingqiao and Reddy, Pramod and Klump, Andrew and Hernandez-Balderrama, Luis H. and Washiyama, Shun and Franke, Alexander and Kirste, Ronny and Hoffmann, Axel and et al.}, year={2016}, month={Sep} }
 @article{alden_guo_kirste_kaess_bryan_troha_bagal_reddy_hernandez-balderrama_franke_et al._2016, title={Fabrication and structural properties of AlN submicron periodic lateral polar structures and waveguides for UV-C applications}, volume={108}, ISSN={["1077-3118"]}, url={https://doi.org/10.1063/1.4955033}, DOI={10.1063/1.4955033}, abstractNote={Periodically poled AlN thin films with submicron domain widths were fabricated for nonlinear applications in the UV-VIS region. A procedure utilizing metalorganic chemical vapor deposition growth of AlN in combination with laser interference lithography was developed for making a nanoscale lateral polarity structure (LPS) with domain size down to 600 nm. The Al-polar and N-polar domains were identified by wet etching the periodic LPS in a potassium hydroxide solution and subsequent scanning electron microscopy (SEM) characterization. Fully coalesced and well-defined vertical interfaces between the adjacent domains were established by cross-sectional SEM. AlN LPSs were mechanically polished and surface roughness with a root mean square value of ∼10 nm over a 90 μm × 90 μm area was achieved. 3.8 μm wide and 650 nm thick AlN LPS waveguides were fabricated. The achieved domain sizes, surface roughness, and waveguides are suitable for second harmonic generation in the UVC spectrum.}, number={26}, journal={APPLIED PHYSICS LETTERS}, publisher={AIP Publishing}, author={Alden, D. and Guo, W. and Kirste, R. and Kaess, F. and Bryan, I. and Troha, T. and Bagal, A. and Reddy, P. and Hernandez-Balderrama, Luis H. and Franke, A. and et al.}, year={2016}, month={Jun} }
 @article{rohrbaugh_hernandez-balderrama_kaess_kirste_collazo_ivanisevic_2016, title={HgNO3 sensitivity of AlGaN/GaN field effect transistors functionalized with phytochelating peptides}, volume={6}, ISSN={["2158-3226"]}, DOI={10.1063/1.4953806}, abstractNote={This study examined the conductance sensitivity of AlGaN/GaN field effect transistors in response to varying Hg/HNO3 solutions. FET surfaces were covalently functionalized with phytochelatin-5 peptides in order to detect Hg in solution. Results showed a resilience of peptide-AlGaN/GaN bonds in the presence of strong HNO3 aliquots, with significant degradation in FET ID signal. However, devices showed strong and varied response to Hg concentrations of 1, 10, 100, and 1000 ppm. The gathered statistically significant results indicate that peptide terminated AlGaN/GaN devices are capable of differentiating between Hg solutions and demonstrate device sensitivity.}, number={6}, journal={AIP ADVANCES}, author={Rohrbaugh, Nathaniel and Hernandez-Balderrama, Luis and Kaess, Felix and Kirste, Ronny and Collazo, Ramon and Ivanisevic, Albena}, year={2016}, month={Jun} }
 @article{franke_hoffmann_kirste_bobea_tweedie_kaess_gerhold_collazo_sitar_2016, title={High reflectivity III-nitride UV-C distributed Bragg reflectors for vertical cavity emitting lasers}, volume={120}, ISSN={["1089-7550"]}, DOI={10.1063/1.4963831}, abstractNote={UV-C distributed Bragg reflectors (DBRs) for vertical cavity surface emitting laser applications and polariton lasers are presented. The structural integrity of up to 25 layer pairs of AlN/Al0.65Ga0.35N DBRs is maintained by balancing the tensile and compressive strain present between the single layers of the multilayer stack grown on top of an Al0.85Ga0.35N template. By comparing the structural and optical properties for DBRs grown on low dislocation density AlN and AlGaN templates, the criteria for plastic relaxation by cracking thick nitride Bragg reflectors are deduced. The critical thickness is found to be limited mainly by the accumulated strain energy during the DBR growth and is only negligibly affected by the dislocations. A reflectance of 97.7% at 273 nm is demonstrated. The demonstrated optical quality and an ability to tune the resonance wavelength of our resonators and microcavity structures open new opportunities for UV-C vertical emitters.}, number={13}, journal={JOURNAL OF APPLIED PHYSICS}, author={Franke, A. and Hoffmann, M. P. and Kirste, R. and Bobea, M. and Tweedie, J. and Kaess, F. and Gerhold, M. and Collazo, R. and Sitar, Z.}, year={2016}, month={Oct} }
 @article{reddy_washiyama_kaess_breckenridge_hernandez-balderrama_haidet_alden_franke_sarkar_kohn_et al._2016, title={High temperature and low pressure chemical vapor deposition of silicon nitride on AlGaN: Band offsets and passivation studies}, volume={119}, ISSN={["1089-7550"]}, url={https://doi.org/10.1063/1.4945775}, DOI={10.1063/1.4945775}, abstractNote={In this work, we employed X-ray photoelectron spectroscopy to determine the band offsets and interface Fermi level at the heterojunction formed by stoichiometric silicon nitride deposited on AlxGa1-xN (of varying Al composition “x”) via low pressure chemical vapor deposition. Silicon nitride is found to form a type II staggered band alignment with AlGaN for all Al compositions (0 ≤ x ≤ 1) and present an electron barrier into AlGaN even at higher Al compositions, where Eg(AlGaN) > Eg(Si3N4). Further, no band bending is observed in AlGaN for x ≤ 0.6 and a reduced band bending (by ∼1 eV in comparison to that at free surface) is observed for x > 0.6. The Fermi level in silicon nitride is found to be at 3 eV with respect to its valence band, which is likely due to silicon (≡Si0/−1) dangling bonds. The presence of band bending for x > 0.6 is seen as a likely consequence of Fermi level alignment at Si3N4/AlGaN hetero-interface and not due to interface states. Photoelectron spectroscopy results are corroborated by current-voltage-temperature and capacitance-voltage measurements. A shift in the interface Fermi level (before band bending at equilibrium) from the conduction band in Si3N4/n-GaN to the valence band in Si3N4/p-GaN is observed, which strongly indicates a reduction in mid-gap interface states. Hence, stoichiometric silicon nitride is found to be a feasible passivation and dielectric insulation material for AlGaN at any composition.}, number={14}, journal={JOURNAL OF APPLIED PHYSICS}, publisher={AIP Publishing}, author={Reddy, Pramod and Washiyama, Shun and Kaess, Felix and Breckenridge, M. Hayden and Hernandez-Balderrama, Luis H. and Haidet, Brian B. and Alden, Dorian and Franke, Alexander and Sarkar, Biplab and Kohn, Erhard and et al.}, year={2016}, month={Apr} }
 @article{reddy_hoffmann_kaess_bryan_bryan_bobea_klump_tweedie_kirste_mita_et al._2016, title={Point defect reduction in wide bandgap semiconductors by defect quasi Fermi level control}, volume={120}, ISSN={["1089-7550"]}, url={https://doi.org/10.1063/1.4967397}, DOI={10.1063/1.4967397}, abstractNote={A theoretical framework for a general approach to reduce point defect density in materials via control of defect quasi Fermi level (dQFL) is presented. The control of dQFL is achieved via excess minority carrier generation. General guidelines for controlling dQFL that lead to a significant reduction in compensating point defects in any doped material is proposed. The framework introduces and incorporates the effects of various factors that control the efficacy of the defect reduction process such as defect level, defect formation energy, bandgap, and excess minority carrier density. Modified formation energy diagrams are proposed, which illustrate the effect of the quasi Fermi level control on the defect formation energies. These formation energy diagrams provide powerful tools to determine the feasibility and requirements to produce the desired reduction in specified point defects. An experimental study of the effect of excess minority carriers on point defect incorporation in GaN and AlGaN shows an excellent quantitative agreement with the theoretical predictions. Illumination at energies larger than the bandgap is employed as a means to generate excess minority carriers. The case studies with CN in Si doped GaN, H and VN in Mg doped GaN and VM-2ON in Si doped Al0.65Ga0.35N revealed a significant reduction in impurities in agreement with the proposed theory. Since compensating point defects control the material performance (this is particularly challenging in wide and ultra wide bandgap materials), dQFL control is a highly promising technique with wide scope and may be utilized to improve the properties of various materials systems and performance of devices based upon them.}, number={18}, journal={JOURNAL OF APPLIED PHYSICS}, publisher={AIP Publishing}, author={Reddy, P. and Hoffmann, M. P. and Kaess, F. and Bryan, Z. and Bryan, I. and Bobea, M. and Klump, A. and Tweedie, J. and Kirste, R. and Mita, S. and et al.}, year={2016}, month={Nov} }
 @article{franke_hoffmann_hernandez-balderrama_kaess_bryan_washiyama_bobea_tweedie_kirste_gerhold_et al._2016, title={Strain engineered high reflectivity DBRs in the deep UV}, volume={9748}, ISSN={["1996-756X"]}, DOI={10.1117/12.2211700}, abstractNote={The maximum achievable reflectivity of current III-nitride Bragg reflectors in the UV-C spectral range is limited due to plastic relaxation of thick multilayer structures. Cracking due to a large mismatch of the thermal expansion and lattice constants between AlxGa1-xN/AlyGa1-yN alloys of different composition and the substrate at the heterointerface is the common failure mode. Strain engineering and strain relaxation concepts by the growth on a strain reduced Al0.85Ga0.15N template and the implementation of low temperature interlayers is demonstrated. A significant enhancement of the maximum reflectivity above 97% at a resonance wavelength of 270 nm due to an increase of the critical thickness of our AlN/Al0.65Ga0.35N DBRs to 1.45 μm (25.5 pairs) prove their potential. By comparing the growth of identical Bragg reflectors on different pseudo-templates, the accumulated mismatch strain energy in the DBR, not the dislocation density provided by the template/substrate, was identified to limit the critical thickness. To further enhance the reflectivity low temperature interlays were implemented into the DBR to partially relief the misfit strain. Relaxation is enabled by the nucleation of small surface domains facilitating misfit dislocation injection and glide. Detailed structural and optical investigations will be conducted to prove the influence of the LT-AlN interlayers on the strain state, structural integrity and reflectivity properties. Coherent growth and no structural and optical degradation of the Bragg mirror properties was observed proving the fully applicability of the relaxation concept to fabricate thick high reflectivity DBR and vertical cavity laser structures.}, journal={GALLIUM NITRIDE MATERIALS AND DEVICES XI}, author={Franke, A. and Hoffmann, P. and Hernandez-Balderrama, L. and Kaess, F. and Bryan, I. and Washiyama, S. and Bobea, M. and Tweedie, J. and Kirste, R. and Gerhold, M. and et al.}, year={2016} }
 @article{kaess_reddy_alden_klump_hernandez-balderrama_franke_kirste_hoffmann_collazo_sitar_et al._2016, title={The effect of illumination power density on carbon defect configuration in silicon doped GaN}, volume={120}, ISSN={["1089-7550"]}, url={https://doi.org/10.1063/1.4972468}, DOI={10.1063/1.4972468}, abstractNote={A study of efficacy of point defect reduction via Fermi level control during growth of GaN:Si as a function of above bandgap illumination power density and hence excess minority carrier density is presented. Electrical characterization revealed an almost two-fold increase in carrier concentration and a three-fold increase in mobility by increasing the illumination power density from 0 to 1 W cm−2, corroborating a decrease in compensation and ionic impurity scattering. The effect was further supported by the photoluminescence studies, which showed a monotonic decrease in yellow luminescence (attributed to CN) as a function of illumination power density. Secondary ion mass spectroscopy studies showed no effect of illumination on the total incorporation of Si or C. Thus, it is concluded that Fermi level management changed the configuration of the C impurity as the CN−1 configuration became energetically less favorable due to excess minority carriers.}, number={23}, journal={JOURNAL OF APPLIED PHYSICS}, publisher={AIP Publishing}, author={Kaess, Felix and Reddy, Pramod and Alden, Dorian and Klump, Andrew and Hernandez-Balderrama, Luis H. and Franke, Alexander and Kirste, Ronny and Hoffmann, Axel and Collazo, Ramón and Sitar, Zlatko and et al.}, year={2016}, month={Dec} }