Abstract
The initial stage of the reaction of oxygen with the surface of layered semiconductor InSe has been studied by XPS. The cleaved surface of InSe does not react with oxygen at room temperature. However, when subjected to Ar ion sputtering, the surface becomes In-rich, and can then be oxidized at room temperature. By heating a sample with a cleaved surface in the atmosphere, the intralayer bonding between Se and In atoms is severed by the formation of In-oxides. In both cases, first, In2O3+x is formed at the surface due to the presence of In–O2 bonds. As oxidation proceeds, In2O3 grows under In2O3+x. In2O3-x is also observed in room-temperature oxidation. No evidence could be found for the presence of Se oxides on the surface under any oxidation conditions. It is found that a heterojunction cell of In2O3–InSe fabricated by the thermal oxidation of InSe exhibits the photovoltaic effect in the visible light region.