Electronic Structure and Optical Properties for Neutral Vacancy Defects in Amorphous Ga₂O₃: A First-Principle Approach

In this work, we establish models of amorphous Ga₂O₃(a-Ga₂O₃) and its five vacancy defects using molecular dynamics and density functional theory. Through hybrid functional calculations, we calculate the electronic structure, defect formation energies, and optical properties of these models. We explain the structural characteristics of the a-Ga₂O₃ model through bond lengths, bond angles, and radial distribution functions. Based on the coordination of oxygen and gallium atoms in the a-Ga₂O₃ model, the defects are divided into three types of oxygen vacancies (V_O) and two types of gallium vacancies (V_Ga). Electronic structure calculations show that V_O will introduce defect states in the band gap, which are contributed by the O 2p states and Ga 4s or 4p states. The V_Ga will induce spin polarization through the dangling bonds of the 2p orbitals of the surrounding oxygen atoms. The defect formation energy of V_O is lower than that of V_Ga, and a-Ga₂O₃ is more likely to exhibit n-type conductivity. The discussion on the changes in the optical absorption spectra and the imaginary part of the dielectric function reveal that different types of V_O and V_Ga cause optical absorption near 3 eV, 2.88 eV, 3.28 eV, 1.6 eV, and 3.45 eV, respectively. The introduction of defects increases the number of absorption peaks and induces a red shift in the absorption edge. This work provides a reference for explaining the influence mechanism of neutral vacancy defects inside a-Ga₂O₃ materials on the electronic structure and optical properties of the material.