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1. Photoluminescence from defects in GaN

   https://doi.org/10.1117/12.2645878  

   Reshchikov, Michael A. (March 2023, Photoluminescence from defects in GaN)

   Morkoç, Hadis; Fujioka, Hiroshi; Schwarz, Ulrich T. (Ed.)

   We present the most recent results of photoluminescence (PL) studies, classification of defects in GaN and their properties. In particular, the yellow luminescence band (labeled YL1) with a maximum at 2.17 eV in undoped GaN grown by most common techniques is unambiguously attributed to the isolated CN acceptor. From the zero-phonon line (ZPL) at 2.59 eV, the /0 level of this acceptor is found at 0.916 eV above the valence band. The PL also reveals the 0/+ level of the CN at 0.33 eV above the valence band, which is responsible for the blue band (BLC), with the ZPL at 3.17 eV. Another yellow band (YL2) with a maximum at 2.3 eV, observed only in GaN grown by the ammonothermal method, is attributed to the VGa3H complex. The nitrogen vacancy (VN) causes the green luminescence (GL2) band. The VN also forms complexes with acceptors such as Mg, Be, and Ca. These complexes are responsible for the red luminescence bands (the RL2 family) in high-resistivity GaN. The results from PL studies are compared with theoretical predictions. Uncertainties in the parameters of defects are discussed. 

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2. Photoluminescence from Be‐Doped GaN Grown by Metal‐Organic Chemical Vapor Deposition

   https://doi.org/10.1002/pssb.202200487  

   Reshchikov, Michael Alexander; Vorobiov, Mykhailo; Andrieiev, Oleksandr; McEwen, Benjamin; Rocco, Emma; Meyers, Vincent; Demchenko, Denis O.; Shahedipour-Sandvik, F. Shadi (December 2022, physica status solidi (b))

   A systematic photoluminescence study of Be‐doped GaN grown by metal‐organic chemical vapor deposition is presented. All Be‐doped samples show the ultraviolet luminescence (UVLBe) band with a maximum at 3.38 eV and the yellow luminescence (YLBe) band with a maximum at ≈2.15 eV in GaN:Be having various concentrations of Be. The UVLBe band is attributed to the shallow state of the BeGa acceptor with a delocalized hole. The YLBe band is caused by a Be‐related defect, possibly the polaronic state of the BeGa acceptor with the charge transition level at 0.3 eV above the valence band. This broad band exhibits unusual properties. In particular, it always shows two steps in its thermal quenching. The second step at T ≈ 200 K is attributed to the emission of holes from the 0.3 eV level to the conduction band. The origin of the first step remains unexplained. 

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3. Fine Structure of the Carbon-Related Blue Luminescence Band in GaN

   https://doi.org/10.3390/solids3020016  

   Reshchikov, Michael A. (June 2022, Solids)

   Photoluminescence studies reveal three CN-related luminescence bands in GaN doped with carbon: the YL1 band at 2.17 eV caused by electron transitions via the −/0 level of the CN, the BLC band at 2.85 eV due to transitions via the 0/+ level of the CN and the BL2 band at 3.0 eV attributed to the CNHi complex. The BLC band studied here has the zero-phonon line at 3.17 eV and a phonon-related fine structure at low temperatures. The 0/+ level of the CN is found at 0.33 ± 0.01 eV above the valence band, in agreement with recent theoretical predictions. These results will help to choose an optimal correction scheme in hybrid functional calculations. 

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4. AlScO ₃ perovskite—An ∼8 eV bandgap oxide predicted to exhibit low small hole polaron ionization energies and p -type conductivity at elevated temperatures

   https://doi.org/10.1063/5.0097204  

   Lee, Cheng-Wei; Gorai, Prashun; Garrity, Emily; Zakutayev, Andriy; Stevanović, Vladan (September 2022, Applied Physics Letters)

   We investigate electronic structure and dopability of an ultrawide bandgap (UWBG) AlScO 3 perovskite, a known high-pressure and long-lived metastable oxide. From first-principles electronic structure calculations, HSE06(+G 0 W 0 ), we find this material to exhibit an indirect bandgap of around 8.0 eV. Defect calculations point to cation and oxygen vacancies as the dominant intrinsic point defects limiting extrinsic doping. While acceptor behaving Al and Sc vacancies prevent n-type doping, oxygen vacancies permit the Fermi energy to reach ∼0.3 eV above the valence band maximum, rendering AlScO 3 p-type dopable. Furthermore, we find that both Mg and Zn could serve as extrinsic p-type dopants. Specifically, Mg is predicted to have achievable net acceptor concentrations of ∼10 17  cm −3 with ionization energy of bound small hole polarons of ∼0.49 eV and free ones below 0.1 eV. These values place AlScO 3 among the UWBG oxides with lowest bound small hole polaron ionization energies, which, as we find, is likely due to large ionic dielectric constant that correlates well with low hole polaron ionization energies across various UWBG oxides. 

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5. Experimental determination of the valence band offsets of ZnGeN2 and (ZnGe)0.94Ga0.12N2 with GaN

   https://doi.org/https://doi.org/10.1088/1361-6463/abee45  

   Karim, Md Rezaul; Noesges, Brent A.; Jayatung, Benthara Hewage; Zhu, Menglin; Hwang, Jinwoo; Lambrecht, Walter R.; Brillson, Leonard J.; Kash, Kathleen; Zhao, Hongping (March 2021, Journal of physics)

   null (Ed.)

   A predicted type-II staggered band alignment with an approximately 1.4 eV valence band offset at the ZnGeN2/GaN heterointerface has inspired novel band-engineered III-N/ZnGeN2 heterostructure-based device designs for applications in high performance optoelectronics. We report on the determination of the valence band offset between metalorganic chemical vapor deposition grown (ZnGe)1−xGa2xN2, for x = 0 and 0.06, and GaN using x-ray photoemission spectroscopy. The valence band of ZnGeN2 was found to lie 1.45–1.65 eV above that of GaN. This result agrees well with the value predicted by first-principles density functional theory calculations using the local density approximation for the potential profile and quasiparticle self-consistent GW calculations of the band edge states relative to the potential. For (ZnGe)0.94Ga0.12N2 the value was determined to be 1.29 eV, ∼10%–20% lower than that of ZnGeN2. The experimental determination of the large band offset between ZnGeN2 and GaN provides promising alternative solutions to address challenges faced with pure III-nitride-based structures and devices. 

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