Quantification of discrete oxide and sulfur layers on sulfur-passivated InAs by XPS

The initial quality and stability in air of InAs(001) surfaces passivated by a weakly-basic solution of thioacetamide (CH3CSNH2) is examined by XPS. The S-passivated InAs(001) surface can be modeled as a sulfur-indium-arsenic ‘layer-cake’ structure, such that characterization requires quantification of both arsenic oxide and sulfur layers that are at most a few monolayers thick. This thickness range complicates the quantitative analysis because neither standard submonolayer nor thick-film models are applicable. Therefore, we develop a discrete-layer model and validate it with angle-resolved XPS data and electron attenuation length (EAL) calculations. We then apply this model to empirically quantify the arsenic oxide and sulfur coverage on the basis of the corresponding XPS intensity ratios. Copyright  2005 John Wiley & Sons, Ltd.