Study of V$_{Ga}^{-2}$ in $\beta $-Ga$_{2}$O$_{3}$ through EPR

Gallium vacancies (V$_{Ga})$ are thought to be common defects found in Ga$_{2}$O$_{3}$. It is important to understand the interaction among defects because charge transfer can cause unwanted effects to happen when Ga$_{2}$O$_{3\, }$is used in high powered devices. Many in the past have attributed problems with Ga$_{2}$O$_{3\, }$to gallium vacancies without being able to observe the vacancy directly. In our work, two neutron-irradiated Ga$_{2}$O$_{3\, }$samples, one as-grown and one Fe-doped, were studied using photo-induced electron paramagnetic resonance (photo EPR), so that charge transfer between various defects could be monitored. In particular, we were able to observe V$_{Ga}^{-2}$ as well as Fe$^{+3}$ in both samples so that potential charge transfer could be seen. The concentrations of Fe$^{+3}$ and V$_{Ga}^{-2}$ were studied under the illumination of various photon energies. The concentration of Fe$^{+3}$ in both samples decreased, which was consistent with the results obtained with non-irradiated samples where V$_{Ga}^{-2}$ was not seen. Significantly, the concentration of V$_{Ga}^{-2}$ in both neutron-irradiated samples did not change. This suggests that the V$_{Ga}^{-2}$ defects are not responsible for the change in the concentration of Fe$^{+3}$ as suggested by others.