An X-ray photoelectron spectroscopy study of the HF etching of native oxides on Ge(111) and Ge(100) surfaces

An X-ray photoelectron spectroscopy (XPS) study of the removal of the native oxides from the Ge(111) and Ge(100) surfaces by hydrofluoric (HF) acid based etch treatments is presented. A cyclic HF etch, water rinse procedure which was repeated a number of times before loading the samples into the XPS chamber was found to be an effective surface oxide removal treatment. In the analysis, germanium 2p and 3d core level data was collected together with C 1s and O 1s data. The Ge 2p and 3d core levels have a wide kinetic energy separation of significantly different escape depths. By consistently curve fitting the chemically shifted oxide peaks for these two core levels it was possible to determine the thickness of the residual oxide coverage on the chemically etched surfaces. Rates of native oxide re-growth as a function of exposure to ambient conditions were also monitored. These oxide regrowth rates were found to be comparable to those reported for hydrogen passivated silicon surfaces suggesting that the chemical procedures used on germanium resulted in the formation of hydrogen terminated surfaces.