Optical transitions of neutral Mg in Mg-doped β-Ga2O3

Gallium oxide when doped with Mg becomes semi-insulating and can be useful for power electronic devices. The present work investigates optical transitions of neutral Mg (${\mathrm{M}\mathrm{g}}_{\mathrm{G}\mathrm{a}}^0$ ) using photoinduced electron paramagnetic resonance spectroscopy, a variation of the traditional optical absorption. Steady-state and time-dependent measurements are carried out at 130 K by illuminating the samples with photon energies from 0.7 to 4.4 eV. Interpretation of the data using a model that incorporates electron–phonon coupling yields a defect transition level that is consistent with the ${\mathrm{M}\mathrm{g}}_{\mathrm{G}\mathrm{a}}^{-/0}$ level obtained from hybrid density functional theory calculations. We conclude that the neutral to negative transition of ${\mathrm{M}\mathrm{g}}_{\mathrm{G}\mathrm{a}}$ that we observe involves an electron transition from the valence band to the defect, and the ${\mathrm{M}\mathrm{g}}_{\mathrm{G}\mathrm{a}}^{-/0}$ level is located 1.2 eV above the valence band maximum, with a relaxation energy of 1.3 eV.