The investigation on the structural distribution of passivated GaAs (100) surface after (NH₄)₂S_x treatment

The qualitative and quantitative structural distribution of HCl- and/or (NH₄)₂S_x-treated GaAs surface was investigated by angle-resolved X-ray photoelectron spectroscopy. Carbon contamination and elemental As layers were observed in HCl-treated GaAs surface. The (NH₄)₂S_X treatment following HCl led to the elemental As replacing the As-S bond. Compared with HCl treatment, the more rugged oscillation of photoelectron intensity of Ga and As was observed according to take-off angle in (NH₄)₂S_x-treated GaAs due to the periodic arrangement of S-passivation layer. The quantitative depth distribution of surface constituents was derived by processing the experimental angular profile and comparing with a simplified layer model. Our results indicate that the distributing order of surface layer on GaAs substrate is a C layer of 5.81 ± 0.54 Å and elemental As layer of 4.57 ± 0.40 Å with HCl treatment, and a C layer of 5.71 ± 0.52 Å and S-passivation layer (As-S) of 4.73 ± 0.40 Å with (NH₄)₂S_x treatment from the surface. Through the analysis of low-energy electron diffraction, the elemental As after HCl treatment was revealed to be randomly distributed and the passivated GaAs surface showed (2 × 1)-reconstructed structure at room temperature with regular distribution of As-S bonds.