Primary intrinsic defects and their charge transition levels in β-Ga2 O3

Abstract

A steady-state photocapacitance (SSPC) setup directly connected to the beamline of a MeV ion implanter is utilized to study primary intrinsic defects in β-Ga2O3 generated by He implantation at cryogenic temperatures (120 K). At low temperatures, the migration of defects is suppressed, and hence the generation of primary intrinsic defects is expected to prevail. SSPC measurements reveal defect-related optical transitions in halide vapor-phase epitaxy (HVPE) -grown β-Ga2O3 thin films with onset energies at 1.3 (T1), 1.7 (T2), 1.9 (T3), 2.6 (T4), 3.7 (T5), and 4.2 eV (T6). T2, T4, T5, and T6 were observed in as-received HVPE-grown β-Ga2O3 thin films, whereby T2 is only sporadically observed. The introduction rates for T3, T4, as well as T6 indicate an origin related to primary intrinsic defects. Notably, T1 and T3 are only observed after He implantation at cryogenic temperatures. Hybrid-functional calculations were performed to estimate the optical absorption cross-section spectra for the gallium (Gai) and oxygen (Oi) interstitials as well as the corresponding vacancies (VGa and VO, respectively), and compared with the measured onsets for optical absorption found by SSPC measurements. Indeed, we propose T3 to be associated with Gai(+/+2) and/or VGaI(-3/-2), while T4 is suggested to be related to VOK(0/+) (K=I, II, III) and/or VGaII(-3/-2). Additionally, several further charge-state transition levels associated with VGaI and VGaII may contribute to T4 and T6. We further studied the kinetics of the defects created with He implantation by exposing the sample to room temperature. The kinetics observed for T3 and T4 further support the proposed assignments of the corresponding defect signatures.