Primary intrinsic defects and their charge transition levels in β–Ga2O3

A steady-state photocapacitance (SSPC) setup directly connected to the beamline of a MeV ion implanter is utilized to study primary intrinsic defects in $\ensuremath{\beta}\text{--}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ 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 $\ensuremath{\beta}\text{--}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ thin films with onset energies at 1.3 $({T}_{1}),$ 1.7 $({T}_{2}),$ 1.9 $({T}_{3}),$ 2.6 $({T}_{4}),$ 3.7 $({T}_{5}),$ and 4.2 eV $({T}_{6})$. ${T}_{2},$ ${T}_{4},$ ${T}_{5},$ and ${T}_{6}$ were observed in as-received HVPE-grown $\ensuremath{\beta}\text{--}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ thin films, whereby ${T}_{2}$ is only sporadically observed. The introduction rates for ${T}_{3},$ ${T}_{4},$ as well as ${T}_{6}$ indicate an origin related to primary intrinsic defects. Notably, ${T}_{1}$ and ${T}_{3}$ 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 $({\mathrm{Ga}}_{\mathrm{i}})$ and oxygen $({\mathrm{O}}_{\mathrm{i}})$ interstitials as well as the corresponding vacancies (${V}_{\mathrm{Ga}}$ and ${V}_{\mathrm{O}}$, respectively), and compared with the measured onsets for optical absorption found by SSPC measurements. Indeed, we propose ${T}_{3}$ to be associated with ${\mathrm{Ga}}_{\mathrm{i}}^{(+/+2)}$ and/or ${V}_{\mathrm{GaI}}^{(\ensuremath{-}3/\ensuremath{-}2)}$, while ${T}_{4}$ is suggested to be related to ${V}_{\text{O}K}^{(0/+)}$ $(K=\mathrm{I}, \mathrm{II}, \mathrm{III})$ and/or ${V}_{\mathrm{GaII}}^{(\ensuremath{-}3/\ensuremath{-}2)}$. Additionally, several further charge-state transition levels associated with ${V}_{\mathrm{GaI}}$ and ${V}_{\mathrm{GaII}}$ may contribute to ${T}_{4}$ and ${T}_{6}$. We further studied the kinetics of the defects created with He implantation by exposing the sample to room temperature. The kinetics observed for ${T}_{3}$ and ${T}_{4}$ further support the proposed assignments of the corresponding defect signatures.