Surface Analysis of Bulk Monocrystalline β-Ga2O3 (-201) via X-ray Photoelectron Spectroscopy

A (-201)-oriented β-Ga2O3 (beta-gallium oxide) single crystal wafer, 2 inches in diameter, was diced into 5 × 5 mm² specimens for surface chemical analysis using X-ray photoelectron spectroscopy (XPS). To ensure accurate surface characterization, both ex situ and in situ pretreatment methods were employed to effectively remove surface contaminants. XPS data collection included a comprehensive survey spectrum and high-resolution core-level scans of Ga 2p, Ga 3s, Ga 3p, Ga 3d, O 1s, and C 1s, along with valence band spectra and Ga LMM and O KLL Auger transitions. The oxidation state identified in all gallium and oxygen photoelectron lines corresponds to Ga³⁺, indicating the presence of the β-Ga2O3 phase. Additionally, organic oxides and hydrocarbons were detected after 300 {degree sign}C UHV annealing, which indicates the presence of strongly bonded species and an elevated number of dangling bonds on the (-201) surface. The Ga and O Auger features further corroborate the oxidation state assignments and offer additional insight into the surface chemical environment of the β- Ga2O3 specimens.