Mid-gap defect levels of gallium oxide

As Ga₂O₃ continues to grow as a material for power electronics, consideration of impurities as well as intrinsic defects becomes essential. Here, Fe- and Mg-doped Ga₂O₃ crystals are irradiated between 0.6 and 4.8 eV, and the effect on Fe³⁺ and Ir⁴⁺ is analyzed at 30 K using electron paramagnetic resonance (EPR). The amount of Fe³⁺ decreases above 2.3 eV which is unlikely a direct ionization of Fe since the Fe^2+/3+ level lies ~0.7 eV below conduction band edge (E_C). Indeed, in Ga₂O₃:Fe, Ir⁴⁺ increases when Fe³⁺ decreases, indicating that the electron excited from Ir³⁺ to E_C is captured by Fe³⁺. However, the decrease for Fe³⁺ is more than the increase for Ir⁴⁺, suggesting Ir alone cannot account for the decrease. Furthermore, in Ga₂O₃:Mg, Fe³⁺ decreases with no change of Ir⁴⁺. These results indicate that other mid-gap defects, likely intrinsic, also contribute electrons to Fe³⁺. The photo-threshold of 2.3 eV suggests that the Ir^3+/4+ and the intrinsic defect levels lie ~2.3 eV from band edges. Moreover, the intrinsic defects are likely oxygen vacancies, V_O, since there are several levels ~2 eV below E_C. Thus, we suggest that the role of intrinsic defects in charge trapping will be important in Ga₂O₃:Fe films grown for device development.