Study of β-Ga₂O₃ Photoluminescence with Above Bandgap Laser Excitation

Ga₂O₃ is being considered as a next generation ultra-wide bandgap semiconductor with promising UV device applications. β-Ga₂O₃ films were grown via RF sputtering and photoluminescence (PL) was performed using 5.1 eV laser excitation, which is above the predicted bandgap of ~4.9eV. Weak UV PL was detected at 4.85eV and 4.20eV. The near band edge (NBE) PL at 4.85eV is consistent with subsequent transmission measurements of the films that showed a bandedge value of 4.85eV. Due to the strong trapping affinity of holes in Ga₂O₃ previously predicted by theory, observation of NBE PL at 4.85eV PL has been deemed unlikely. We speculate that the laser intensity employed in our experiments was sufficient to create a small density of free holes enabling NBE in Ga₂O₃. The 4.20eV PL emission exhibits peak shifts up to ~100meV under different annealing environments. Strong UV emissions were also observed at 3.14eV and 3.56eV, which have been attributed to donor-acceptor recombination and self-trapped holes, respectively. Emission due to self-trapped holes was not detected when sub-bandgap laser excitation of 3.8eV was utilized.