@article{alden_troha_kirste_mita_guo_hoffmann_zgonik_collazo_sitar_2019, title={Quasi-phase-matched second harmonic generation of UV light using AlN waveguides}, volume={114}, ISSN={["1077-3118"]}, DOI={10.1063/1.5087058}, abstractNote={As an alternative to electrically injected diodes, UV light emission can be obtained via second harmonic generation (SHG). In weakly birefringent materials such as aluminum nitride (AlN), the phase matching of the driving and second harmonic waves can be achieved by the quasi-phase-matching (QPM) technique, where the polarity of the material is periodically changed commensurate with the coherence wavelength. QPM also allows the use of the highest nonlinear susceptibility, and therefore, higher conversion efficiencies are possible. In this work, the QPM SHG of UV light in AlN lateral polar structure-based waveguides is demonstrated. The peak intensity of the frequency doubled laser light was measured at 344 nm and 472 nm wavelengths, in agreement with dispersion-based theoretical predictions. These results confirm the potential of III-nitride-based lateral polar structures for quasi-phase-matched nonlinear optics and for frequency doubling media for UV light generation.As an alternative to electrically injected diodes, UV light emission can be obtained via second harmonic generation (SHG). In weakly birefringent materials such as aluminum nitride (AlN), the phase matching of the driving and second harmonic waves can be achieved by the quasi-phase-matching (QPM) technique, where the polarity of the material is periodically changed commensurate with the coherence wavelength. QPM also allows the use of the highest nonlinear susceptibility, and therefore, higher conversion efficiencies are possible. In this work, the QPM SHG of UV light in AlN lateral polar structure-based waveguides is demonstrated. The peak intensity of the frequency doubled laser light was measured at 344 nm and 472 nm wavelengths, in agreement with dispersion-based theoretical predictions. These results confirm the potential of III-nitride-based lateral polar structures for quasi-phase-matched nonlinear optics and for frequency doubling media for UV light generation.}, number={10}, journal={APPLIED PHYSICS LETTERS}, author={Alden, Dorian and Troha, Tinkara and Kirste, Ronny and Mita, Seiji and Guo, Qiang and Hoffmann, Axel and Zgonik, Marko and Collazo, Ramon and Sitar, Zlatko}, year={2019}, month={Mar} }
 @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{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{abate_seidlitz_fali_gamage_babicheva_yakovlev_stockman_collazo_alden_dietz_2016, title={Nanoscopy of Phase Separation in InxGa1-xN Alloys}, volume={8}, ISSN={["1944-8244"]}, DOI={10.1021/acsami.6b06766}, abstractNote={Phase separations in ternary/multinary semiconductor alloys is a major challenge that limits optical and electronic internal device efficiency. We have found ubiquitous local phase separation in In1-xGaxN alloys that persists to nanoscale spatial extent by employing high-resolution nanoimaging technique. We lithographically patterned InN/sapphire substrates with nanolayers of In1-xGaxN down to few atomic layers thick that enabled us to calibrate the near-field infrared response of the semiconductor nanolayers as a function of composition and thickness. We also developed an advanced theoretical approach that considers the full geometry of the probe tip and all the sample and substrate layers. Combining experiment and theory, we identified and quantified phase separation in epitaxially grown individual nanoalloys. We found that the scale of the phase separation varies widely from particle to particle ranging from all Ga- to all In-rich regions and covering everything in between. We have found that between 20 and 25% of particles show some level of Ga-rich phase separation over the entire sample region, which is in qualitative agreement with the known phase diagram of In1-xGaxN system.}, number={35}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Abate, Yohannes and Seidlitz, Daniel and Fali, Alireza and Gamage, Sampath and Babicheva, Viktoriia and Yakovlev, Vladislav S. and Stockman, Mark I. and Collazo, Ramon and Alden, Dorian and Dietz, Nikolaus}, year={2016}, month={Sep}, pages={23160–23166} }
 @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} }
 @article{troha_rigler_alden_bryan_guo_kirste_mita_gerhold_collazo_sitar_et al._2016, title={UV second harmonic generation in AlN waveguides with modal phase matching}, volume={6}, ISSN={["2159-3930"]}, DOI={10.1364/ome.6.002014}, abstractNote={AlN waveguides on sapphire substrates were fabricated from AlN films grown by metalorganic chemical vapor deposition. By tuning the wavelength of the pump light we demonstrated a second harmonic generation in the UV at 306, 331, and 356 nm using the d33 coefficient and modal dispersion phase matching (MDPM). A theoretical model for MDPM with two- and three-mode interaction in planar waveguides was used to explain the results. Its essential component describes the interaction of two, possibly different, waveguide modes at the fundamental frequency that excite the third mode at doubled frequency. The experimental results were found to agree well with the theoretical model. This work confirmed the application potential of high-quality AlN films as waveguides for nonlinear processes.}, number={6}, journal={OPTICAL MATERIALS EXPRESS}, author={Troha, T. and Rigler, M. and Alden, D. and Bryan, I. and Guo, W. and Kirste, R. and Mita, S. and Gerhold, M. D. and Collazo, R. and Sitar, Z. and et al.}, year={2016}, month={Jun}, pages={2014–2023} }
 @inproceedings{seidlitz_fali_kankanamge_alden_collazo_hoffmann_dietz_abate, title={Infrared nanoscopy of In-rich InGaN epilayers (Conference Presentation)}, volume={9954}, booktitle={Fifteenth international conference on solid state lighting and led-based illumination systems}, author={Seidlitz, D. and Fali, A. and Kankanamge, I. S. M. and Alden, D. and Collazo, R. and Hoffmann, A. and Dietz, N. and Abate, Y.} }
 @inproceedings{alden_bryan_gaddy_bryan_callsen_koukitu_kumagai_hoffmann_irving_sitar_et al., title={On the origin of the 4.7 eV absorption and 2.8 eV emission bands in bulk AlN substrates}, volume={72}, number={5}, booktitle={Wide bandgap semiconductor materials and devices 17}, author={Alden, D. and Bryan, Z. and Gaddy, B. E. and Bryan, I. and Callsen, G. and Koukitu, A. and Kumagai, Y. and Hoffmann, A. and Irving, D. L. and Sitar, Z. and et al.}, pages={31–40} }