Formation and control of the E*2 center in implanted β-Ga2O3 by reverse-bias and zero-bias annealing

Abstract

Deep-level transient spectroscopy measurements are conducted on β-Ga2O3 thin-films implanted with helium and hydrogen (H) to study the formation of the defect level E*2 (A = 0.71 eV) during heat treatments under an applied reverse-bias voltage (reverse-bias annealing). The formation of 2 during reverse-bias annealing is a thermally-activated process exhibiting an activation energy of around 1.0 eV to 1.3 eV, and applying larger reverse-bias voltages during the heat treatment results in a larger concentration of E*2. In contrast, heat treatments without an applied reverse-bias voltage (zero-bias annealing) can be used to decrease the E*2 concentration. The removal of E*2 is more pronounced if zero-bias anneals are performed in the presence of H. A scenario for the formation of E*2 is proposed, where the main effect of reverse-bias annealing is an effective change in the Fermi-level position within the space-charge region, and where E*2 is related to a defect complex involving intrinsic defects that exhibits several different configurations whose relative formation energies depend on the Fermi-level position. One of these configurations gives rise to E*2, and is more likely to form if the Fermi-level position is further away from the conduction band edge. The defect complex related to E*2 can become hydrogenated, and the corresponding hydrogenated complex is likely to form when the Fermi level is close to the conduction band edge. Di-vacancy defects formed by oxygen and gallium vacancies (VO-VGa) fulfill several of these requirements, and are proposed as potential candidates for E*2.