Surface dipole formation and electronic structure evolution on <i>β</i> -Ga2O3

The surface electronic structure of Ga2O3 critically influences its metal/Ga2O3 contact and semiconductor/Ga2O3 interface property, as well as the overall device performance. However, the fundamental surface properties, e.g., band bending and vacuum bending are not yet fully understood, especially under surface treatment procedure. In this study, we systematically investigate the surface evolution of both (−201)- and (010)-oriented β-Ga2O3 using x-ray photoelectron spectroscopy in conjunction in situ Ar+ ion sputtering. Both surfaces initially exhibit significantly reduced work functions following widely unitized Piranha treatment, primarily due to the formation of inward-pointing surface dipoles arising from oxygen-rich terminations. As ion etching proceeds, the work function gradually increases and ultimately saturates once the dipole layer is fully removed. The Ga:O ratios and O 1s peak deconvolution indicates a gradual reduction in gallium hydroxyl (Ga-OH) groups, returning the surface toward stoichiometric composition. Quantitative analysis demonstrates that vacuum level bending (∼0.9 eV) far exceeds band bending (∼0.2 eV), highlighting a dipole-dominated mechanism. These findings provide crucial insights into the intricate interplay between surface chemistry and electronic structure, establishing a strategy for rational band alignment engineering via surface dipole control and optimizing interfaces in Ga2O3-based electronic and optoelectronics devices.