Temperature Response of the Optical Properties of Ultra-Wide Bandgap β-Ga₂O₃ Films

β-Ga₂O₃ is a semiconductor with ultra-wide bandgap at ~ 5 eV that is thermodynamically stable up to 1800 C which enables its application in high temperature devices. This research focuses on the temperature response of the bandgap and the UV photoluminescence (PL) at 77 K to 620 K.  β-Ga₂O₃ films were grown using a sputtering technique and analyzed via transmission, Raman scattering, and UV- PL. The bandgap exhibited a redshift ~ 200 meV as a function of temperature; its room temperature value is 4.85 eV. The electron-phonon interaction model pointed to a low energy phonon, ~ 31 meV, that is involved in the thermal properties of the bandgap. Urbach analysis indicated that defects are the dominant mechanism controlling the band edge characteristics even at elevated temperatures where phonon dominance is usually expected. Defects are attributed to the disordered forms of graphite that were detected via Raman scattering, and to the granular morphology of the film. A deep-UV laser with an above-bandgap exaction was employed to map the PL. The highly resolved spectra show a strong emission ~ 3.56 eV attributed to self-trapped holes (STH) that exhibited a weak temperature dependance thus implying a strong localization. A low intensity PL was found at 4.85 eV that agrees with the value of the bandgap and is attributed to free e-h recombination whose intensity is impeded by the STH.