Transition levels for impurities in β-Ga₂O₃

Bulk Ga₂O₃ is of interest for both electronic and optical applications. However, the large number of different impurities often complicates understanding of the basic material properties. Confusion can be minimized by directly monitoring individual impurities using photo-induced electron paramagnetic resonance (EPR). Specifically, the present work tests the validity of several proposed defect levels in Fe-doped and Mg-doped β-Ga₂O₃ crystals by identifying each impurity, Fe³⁺, Mg⁰, and Ir⁴⁺ with an EPR spectrum. The EPR intensity for the impurity is monitored during illumination from 1500 to 300 nm at 30 K or 130 K, and changes are associated with ionization. A photo-threshold between 2.0 and 2.3 eV where Ir⁴⁺ increases and Fe³⁺ decreases is assigned to the Ir^3+/4+ defect level, and one between1.2 and 1.5 eV where Fe³⁺ increases is assigned the Fe^2+/3+ level after consideration of the lattice relaxation. Ongoing study of the Mg-doped samples indicates that Mg⁰ decreases between 1.6 and 1.9 eV, consistent with reported levels for Mg^-/0; however the photon energy dependence for the generation of the neutral Mg⁰ is not yet clear. The presentation will describe procedure and analysis details, particularly for the curious case of neutral Mg.