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1. Photoluminescence from Defects in Be‐Doped GaN

   https://doi.org/10.1002/pssb.202400656  

   Reshchikov, Michael_Alexander; McEwen, Benjamin; Shahedipour‐Sandvik, Shadi (February 2025, physica status solidi (b))

   While GaN is a crucial semiconductor material for bright light‐emitting devices, fabrication of p‐type GaN remains challenging since the Mg acceptor commonly used for p‐type doping is not shallow enough. Doping of GaN with Be is a promising path, yet no reliable p‐type GaN has been achieved by Be doping so far. One of the reasons is a poor understanding of point defects in Be‐doped GaN that can be studied by photoluminescence (PL). The yellow (YL_Be) band at 2.15 eV is the dominant PL band in Be‐doped GaN. In this work, a blue PL band named the BL_Beband is discovered. It has a maximum at 2.6 eV and a lifetime of 0.8 μs at temperatures below 100 K. The BL_Beband is observed in GaN samples with relatively high concentrations of Be (>10¹⁸ cm⁻³). Both the YL_Beand BL_Bebands likely originate from the isolated Be_Gadefect, namely from electron transitions via the −/0 and 0/+ thermodynamic transition levels of the Be_Ga. The 0/+ transition level is located at 0.1–0.2 eV above the valence band. Other broad PL bands in Be‐doped GaN were also observed and preliminarily attributed to Be‐containing complexes. 

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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 (UVL_Be) band with a maximum at 3.38 eV and the yellow luminescence (YL_Be) band with a maximum at ≈2.15 eV in GaN:Be having various concentrations of Be. The UVL_Beband is attributed to the shallow state of the Be_Gaacceptor with a delocalized hole. The YL_Beband is caused by a Be‐related defect, possibly the polaronic state of the Be_Gaacceptor 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 atT ≈ 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. On the Origin of the Yellow Luminescence Band in GaN

   https://doi.org/10.1002/pssb.202200488  

   Reshchikov, Michael A. (December 2022, physica status solidi (b))

   The yellow luminescence (YL) band with a maximum at 2.2 eV is the dominant defect‐related luminescence in unintentionally doped GaN. The discovery of the mechanism responsible for this luminescence band and related defects in GaN took many years. Eventually, a consensus has been reached that the C_Nacceptor is the source of the YL band (the YL1 band) in GaN samples grown by several techniques. Previously suggested candidates, such as V_Ga, V_GaO_N, C_NO_N, and C_NSi_Ga, should be discarded. At the same time, other defects (such as the V_N, Be_Ga, and Ca_Ga) may cause luminescence bands with positions and shapes not much different from the YL1 band. In GaN containing high concentrations of gallium vacancies, oxygen, and hydrogen, complexes containing these species may also contribute in the red–yellow part of the photoluminescence spectrum. The main controversies related to the YL band are resolved. 

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5. Thermal annealing of GaN implanted with Be

   https://doi.org/10.1063/5.0080060  

   Reshchikov, M. A.; Andrieiev, O.; Vorobiov, M.; Ye, D.; Demchenko, D. O.; Sierakowski, K.; Bockowski, M.; McEwen, B.; Meyers, V.; Shahedipour-Sandvik, F. (March 2022, Journal of Applied Physics)

   GaN samples were implanted with Be and annealed in different conditions in order to activate the shallow Be_Gaacceptor. Low-temperature photoluminescence spectra were studied to find Be_Ga-related defects in the implanted samples. A yellow band with a maximum at about 2.2 eV (the YL_Beband) was observed in nearly all samples protected with an AlN cap during the annealing and in samples annealed under ultrahigh N₂pressure. A green band with a maximum at 2.35 eV (the GL2 band), attributed to the nitrogen vacancy, was the dominant defect-related luminescence band in GaN samples annealed without a protective AlN layer. The ultraviolet luminescence (UVL_Be) band with a maximum at 3.38 eV attributed to the shallow Be_Gaacceptor with the ionization energy of 0.113 eV appeared in implanted samples only after annealing at high temperatures and ultrahigh N₂pressure. This is the first observation of the UVL_Beband in Be-implanted GaN, indicating successful activation of the Be_Gaacceptor. 

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