Optical and structural characterization of high crystalline β-Ga2O3 films prepared using an RF magnetron sputtering

β-Ga2O3 films have been prepared on sapphire (0001) substrate using an RF magnetron sputtering. The highly oriented β-Ga2O3 films with a high crystallinity could be obtained at Ts above 700 °C. The sputtered film in pure Ar showed a low optical band-gap and a strong optical absorption in UV and visible region, possibly due to non-stoichiometry, oxygen-deficiency. Raman modes of β-Ga2O3 started to evolve at Ts of 400 °C and then, were clearly defined and dominant at Ts above 600 °C in a good consistence with XRD result. In the PL spectra at Ts above 600 °C, UV emission peaked at 3.75 eV and red-emission composed of broad band and sharp peaks were predominant. These emissions are the first report in PL spectra of β-Ga2O3 and have been tentatively assigned to high energy excitons caused by electrons trapped with holes at deeper acceptor level, and optical transition between deep donor level and delocalized/clustered acceptor levels, respectively.