Defect energy levels in monoclinic β-Ga2O3

The defect levels in semiconductor are crucial to the performance of related devices. However, the positions of the defect levels in monoclinic β-Ga2O3, such as that for oxygen vacancy (VO), Ga–O divacancy, and self-trapped hole (STH), are still controversial. In this paper, we systematically investigated the photoluminescence and photoluminescence excitation spectra of undoped, Si-doped, and Mg-doped β-Ga2O3 single crystals grown by the edge-defined film-fed growth method. It is found that the oxygen vacancies are deep donors and their levels are related to the coordinations of the vacancies. For each crystal, the recombination between VO and Ga–O divacancy levels is the origin of the blue emission, and the red emission originates from the transition from VO to STH levels. The location of STH level is also related to the geometrical position of oxygen. For the Si-doped crystal, no red emission is observed due to the annihilation of STHs. While a Mg impurity level is produced at ∼1 eV above the valence band maximum, which causes an extra red emission in the spectra of Mg-doped crystal. Our results strongly support the recent theoretical results obtained via first-principle calculations [Q. D. Ho et al., Phys. Rev. B 97 (2018) 115163] and could be benefit for designing β-Ga2O3 related devices.