Adsorption of H2S on GaP(001) surface and passivation effects studied by AES, LEED and XPS

Adsorption of H2S on the GaP(001)-(4 × 2) clean surface and passivation of the surface to oxidation have been studied using Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). The amount of sulfur adsorbed on the surface is increased by electron-beam irradiation. It is suggested that the increase is caused by activation of H2S and the breaking of GaP bonds. The multi-layers of sulfur on the surface are formed during the irradiation. Three kinds of chemical states of adsorbed sulfur at the multi-layers are suggested to correspond to a SGa bond at the first and second layers, and a SS bond. The surface with a (1 × 1) structure and with multi-layers of sulfur are reconstructed to a (1 × 2) structure by annealing at about 450 and 600°C, respectively. It is found that the amount of oxygen adsorbed on a GaP(001)-(1 × 2)S surface is much lower than on the clean surface, which implies that the GaP(001) surface is well passivated by H2S adsorption.