Formation and control of the E2* center in implanted b-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 E2 lowast (EA = 0.71 eV) during heat treatments under an applied reverse-bias voltage (reverse-bias annealing). The formation of E2 lowast 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 E2 lowast. In contrast, heat treatments without an applied reverse-bias voltage (zero-bias annealing) can be used to decrease the E2 lowast concentration. The removal of E2 lowast is more pronounced if zero-bias anneals are performed in the presence of H. A scenario for the formation of E2 lowast 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 E2 lowast 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 E2 lowast, and is more likely to form if the Fermi-level position is further away from the conduction band edge. The defect complex related to E2 lowast 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 E2 lowast.