Computational Study of LiGaO₂ Electron Paramagnetic Resonance Spectra of Li and Ga Vacancies

LiGaO₂ is an ultra-wide-band-gap material with a wurtzite-like crystal structure and band gap of 5.3 eV. Electron paramagnetic resonance (EPR) experiments on irradiated samples of this material were recently published by Lenyk et al. (J. Appl. Phys. 124, 135702, 2018). In the present work, density functinal theory (DFT) calculations are carried out of the Ga and Li vacancies using the DFT+U approach in the charge states which carry an unpaired spin. In both vacancies the p-hole is located on one oxygen atom adjacent to the vacancy. Apical O and basal plane O are considered. The magnetic resonance parameters of the defects are determined using the Gauge Including Projector Augmented Wave (GIPAW) method. The EPR spectra of V_Ga^2- is characterized by a quasi-isotropic superhyperfine interaction with one Ga nucleus and for the apical O spin gives a g-tensor with maximum oriented along b axis. For V_Li⁰ there is a quasi-isotropic superhyperfine interaction with two Ga nuclei and the g-tensor maximum is along c for the basal plane O spin. Both of these are in agreement with experiment but we predict also the g-tensors for the other possible localization of the spins. The energy ordering and transition levels for the different models will be discussed.