Defect induced site-selective self-trapped holes and their optical fingerprints in β-Ga2O3.

Abstract The monoclinic β-Ga2O3 exhibits strongly linearly polarized ultraviolet luminescence, associated to native defects; however, the microscopic relationship between the tetrahedral (VGaI) and octahedral (VGaII) native gallium vacancies and the observed optical dichroism remains unresolved. By considering spin-polarized hybrid density-functional theory, we demonstrate that both gallium vacancies act as efficient traps for oxygen-centered self-trapped holes (STHs). Specifically, VGaI and VGaII favor different STH configurations localized on inequivalent neighboring oxygen sites, that lead to spin-polarized weakly dispersive defect states closed to the valence-band maximum. These energy levels allow for defect-specific optical transitions to the conduction-band. Thus, the anisotropic real-space STH wavefunctions, dictated by the local Ga-O connectivity, induces a pronounced vacancy-dependent linear dichroism in the near-edge optical response. In this work we establish a correlation between the polarization-resolved optical spectra and the particular spatial distribution of STH generated in presence of the two possible gallium-vacancies in β-Ga2O3 to provide a unified microscopic interpretation of its UV defect luminescence.