XPS intensity analysis for assessment of thickness and composition of thin overlayer films: Application to chemically etched GaAs(100) surfaces

Abstract

Abstract Quantification by XPS intensity analysis of thin multicomponent overlayers, like the native oxides forming on compound semiconductor surfaces, is discussed in some detail. In particular, the advantage of exploiting the attenuated emission from substrate core levels with different probing depths is emphasized, in order to obtain a precise measure for the overlayer thickness dimension. For GaAs(100) treated with different chemical etches, estimates are obtained for the thickness of the native surface oxide formed after exposure to air, of 6–8 Å. The elemental composition of the surface oxide is close to the stoichiometric metal: oxygen ratio of the bulk oxides Ga 2 O 3 and As 2 O 3 , in perfect agreement with the measured core‐level shifts (1.4 ± 0.2 and 3.0 ± 0.1 eV for the Ga and As 2p levels, respectively). On a CF 4 plasma‐etched sample, a surface reaction layer of gallium fluoride was found with a composition close to GaF 2 and an estimated thickness of ∼23 Å. This paper also discusses how to determine the kinetic energy dependence of the electron escape depth, expressed in terms of an exponent m (γ E m ), by working out consistent estimates for the surface oxide (fluoride) thickness via two different approaches. Values for m are obtained in the range 0.5–0.6, in excellent agreement with previously reported data on electron escape depth for semiconductors.