Optical transitions of gallium vacancies in neutron irradiated β-Ga2O3

Investigation of intrinsic defects such as gallium vacancies (V_Ga) and their interactions with extrinsic defects like Fe in β-Ga₂O₃ is crucial for the development of devices. Photoinduced electron paramagnetic resonance (photo-EPR) experiments are performed at room temperature and 30 K by illuminating neutron irradiated Fe-doped and unintentionally doped β-Ga₂O₃ crystals with LEDs from 0.7 to 4.7 eV, and interactions between V_Ga and other defects such as Fe are investigated. 30 K measurements indicate small photoinduced changes in the amount of ${\mathrm{V}}_{\mathrm{Ga}}^{2-}$ , but the photothreshold suggests little or no interaction with Fe. Rather, the decrease of ${\mathrm{V}}_{\mathrm{Ga}}^{2-}$ is accompanied by the emergence of self-trapped holes (STHs), indicating that the stability of the STH is critical to the ${\mathrm{V}}_{\mathrm{Ga}}^{2-}$ optical transition. We suggest the decrease of ${\mathrm{V}}_{\mathrm{Ga}}^{2-}$ is due to excitation of electrons from valence band maximum to the defect. The resulting hole is captured at an oxygen atom to form STH. By performing a systematic photo-EPR study of gallium vacancies, we show that the intrinsic defect, V_Ga, does not interact with extrinsic defects, Fe or Ir. Instead, V_Ga contributes to the stability of the STH.