Electrical and Optical Properties of Beryllium Deep Acceptors in GaN
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https://doi.org/10.1007/s11664-020-08472-5 Ó 2020 The Minerals, Metals & Materials Society
Electrical and Optical Properties of Beryllium Deep Acceptors in GaN SHAN JIN,1,2 XUEFEI LI,1,2 WENXIAN YANG,2 YUKUN ZHAO,2 LIFENG BIAN,1,2,3 and SHULONG LU2 1.—School of Nano-Tech and Nano-Bionics, University of Science and Technology of China, Hefei 230026, China. 2.—Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215125, China. 3.—e-mail: [email protected]
Beryllium (Be) may be a substitute for GaN p-type dopant magnesium due to its smaller atomic size and higher electronegativity. However, Be has been shown to be a deep acceptor in recent experiments. By using the hybrid functional based on density functional theory (DFT), we predict two acceptors with symmetric-broken configurations (SB1 and SB2) in neutral charge state of Be substitutional doping, and analyze their optical and electronic properties. The ionization energy and emission peak of the symmetric-broken configuration SB2 are almost the same as the ground-state (neutral charge state) configuration SB1. Our work provides a comprehensive understanding of the deep acceptor behavior of Be in wurtzite GaN. Key words: Density functional theory, Be-doping, electronic structure, optoelectronics
INTRODUCTION p-type gallium nitride (GaN) materials are essential for the formation of p–n junctions and pcontacts in blue-light emitting diodes (LEDs)1 and heterojunction bipolar transistors (HBTs).2 As for now, magnesium (Mg) is the only successful dopant for the p-type doping of GaN, but the doping efficiency is still very limited. Be is thought to be a better p-type dopant for GaN due to its shallower acceptor level than that of Mg. However, a deep acceptor behavior of Be has been found in recent theoretical3,4 and experimental5,6 investigations. The low ionization energy of the Be acceptor was reported in early experiments, which was based on the thought that the near-edge photoluminescence signals are caused by the shallow Be acceptor.7,8 Nevertheless, a deeper (0/-1) transition of the Berelated acceptor of 0.7 eV (ionization energy) above the valence band maximum is found in recent measurements of the photo-induced electron
(Received February 17, 2020; accepted September 5, 2020)
paramagnetic resonance (EPR), and a yellow photoluminescence (PL) peak of 2.2 eV is predicted.5,6 Meanwhile, In an optically detected magnetic resonance (ODMR) measurement by Glaser et al., the yellow PL peak (2.25 eV) has an approximately isotropic g-tensor but with anisotropy (gjj = 1.991 and g? = 1.995, very small shift from the free electron g value of 2.0023) under the magnetic field applied perpendicular to and parallel to the c-axis direction.6 It is considered that the response feature may come from deep acceptors, which lacks a theoretical explanation and microscopic mechanism for further discussion. The previous theoretical calculations also predicted that Be may be a shallow acceptor with a lo
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