Photoelectron spectroscopic study of electronic states and surface structure of an in situ cleaved In2O3 (111) single crystal

Abstract

Surface electronic states and band-bending behavior of a melt-grown (111)-plane In2O3 single crystal were investigated using X-ray photoelectron spectroscopy (XPES). The In2O3 single crystal was cleaved under vacuum conditions below 5 × 10-5 Pa, and loaded to a measurement chamber with a vacuum level of approximately 5 × 10-7 Pa. After cleaving, density reduction of in-gap states relating to oxygen vacancies was confirmed. Nevertheless, the cleaved surface had a surface electron accumulation layer with the surface Fermi level pinned at approximately 0.76 eV above the conduction band minimum. The bulk and surface carrier density were estimated as 3.9 × 1017 and 6.0 × 1019 cm-3 respectively by combining the XPES result and the Poisson-Schrödinger solutions. Scanning nonlinear dielectric microscopy indicated a higher carrier density at the (100) surface than that at the (111) surface, suggesting a crystallographic plane dependence which may originate in defects relating to the dipole and surface instability of the In2O3 surface.