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 onβ-Ga2O3thin-filmsimplanted with helium and hydrogen (H) to study the formation of the defect levelE∗2(EA=0.71 eV) during heat treatments under an applied reverse-bias voltage (reverse-biasannealing). The formation ofE∗2during reverse-bias annealing is a thermally-activated processexhibiting an activation energy of around 1.0 eV to 1.3 eV, and applying larger reverse-biasvoltages during the heat treatment results in a larger concentration ofE∗2. In contrast, heattreatments without an applied reverse-bias voltage (zero-bias annealing) can be used to decreasetheE∗2concentration. The removal ofE∗2is more pronounced if zero-bias anneals are performedin the presence of H. A scenario for the formation ofE∗2is proposed, where the main effect ofreverse-bias annealing is an effective change in the Fermi-level position within the space-chargeregion, and whereE∗2is related to a defect complex involving intrinsic defects that exhibitsseveral different configurations whose relative formation energies depend on the Fermi-levelposition. One of these configurations gives rise toE∗2, and is more likely to form if theFermi-level position is further away from the conduction band edge. The defect complex relatedtoE∗2can become hydrogenated, and the corresponding hydrogenated complex is likely to formwhen the Fermi level is close to the conduction band edge. Di-vacancy defects formed byoxygen and gallium vacancies (VO−VGa) fulfill several of these requirements, and are proposedas potential candidates forE∗2.