Liquid-Phase Adsorption of Sulfur on Germanium: Reaction Mechanism and Atomic Geometry

Abstract

We present a fundamental study of the monolayer adsorption of sulfur on Ge(100) surfaces from aqueous (NH4)(2)S solution. This treatment shows promising perspectives for the passivation of high-mobility semiconductor surfaces and is therefore presently of great technological importance. The adsorption mechanisms as well as the adsorption geometry are thoroughly investigated at the atomic scale, by both experiment and theory, applying X-ray absorption spectroscopy and molecular dynamics simulations. Our findings indicate that sulfidation in solution results in the formation of Ge-S-Ge bridges along the [110] direction, with no indication for -SH surface groups. A-S-Ge bond length of 2.25 +/- 0.05 angstrom was deduced, which is affected by the chemical environment of the sulfur atoms, i.e., by residual surface oxides. Our study provides novel insights into the surface termination and atomic structure of (NH4)(2)S-treated Ge(100) surfaces and discusses possible differences from in situ sulfur adsorption methods such as H2S or S-2 exposure.