High-temperature annealing induced electrical compensation in UID and Sn doped <i>β</i>-Ga2O3 bulk samples: The role of VGa–Sn complexes

By electron paramagnetic resonance (EPR) and photoluminescence spectroscopy, we have investigated the effect of high-temperature annealing under oxygen atmosphere on the electrical and defect properties of unintentionally doped (UID) and highly doped (Sn) n-type bulk samples of β-Ga2O3. The EPR analysis of the shallow donor concentration shows efficient electrical compensation in the Sn doped β-Ga2O3 samples but only marginal changes for the UID samples. In the Sn doped samples, we observe the formation of a Ga vacancy related acceptor defect responsible for the compensation. Its spin Hamiltonian parameters are electron spin S = 1/2, g-tensor g11 = 2.0423, g22 = 2.0160, g33 = 2.0024, and hyperfine interaction (hf) with two equivalent Ga atoms with A(69Ga) = 28 G. To identify its microscopic structure, we have performed first-principles calculations of the EPR parameters and the associated photoluminescence spectra of different Ga vacancy–Sn donor complexes, including a simple nearest neighbor pair VGa–SnGa. From these calculations, we attribute this VGa defect to a negatively charged split vacancy complex VGa1–Snib–VGa1. This VGa defect is different from the irradiation induced VGa center.