RF magnetron sputtering of Ga2 O3 thin films: Analysis of oxygen flow rate impact on stoichiometry, structural, optical characteristics, and energy band alignments

This study employed RF magnetron sputtering with a ceramic stoichiometric Gallium oxide (Ga2O3) target to deposit thin films on c-sapphire substrates, investigating the impact of varying O2 flow rates on the stoichiometry, structural properties, optical characteristics, and band alignment of the fl-Ga2O3 films. A significant issue is the preferential sputtering of Ga from the Ga2O3 target, which can lead to a deviation from the desired stoichiometry in the deposited films. To address this issue, an effective solution is an appropriate amount of O2 into the Ar process gas at 400 degrees C that is utilized during the deposition method. In this case, the X-ray diffraction (XRD) analysis demonstrated that the deposited thin films have a uniform and well-defined single crystalline structure and display a strong (-401) orientation. fl-Ga2O3 thin films exhibit high transmittance in the visible region and possess a wide band gap, as determined by UV-Visible spectroscopy. The sample deposited with a flow rate of 3 sccm O2 displayed the desired single-crystalline structure. This result also demonstrated that excessive oxygen impacts the crystallization of the thin film, as verified through X-ray diffraction (XRD) analysis. Furthermore, we explain how oxygen flow rates affect the alignment of the bands in fl-Ga2O3/Al2O3 heterojunctions as measured by XPS and UPS analysis, which has not yet been reported. The results of our study reveal that O2 flow rates of 3 sccm, 5 sccm, and 10 sccm increased valence band offset (VBO) by 28.5%, 8.1%, and 10.2% respectively, compared to 0 sccm, impacting vertical devices.