An XPS study of sputtered a-Si,Ge alloys

Abstract

The x-ray photoelectron (XPS) spectra of amorphous silicon–germanium alloys (a-Si,Ge) were measured using Al Kα excitation. Homogeneity of the alloy samples was established through measurements of the optical absorption edge, the Raman scattering, and the electron energy loss (EELS) spectra. We have studied in detail the binding energies (BE) of the Si 2 p and Ge 3d core states, and in particular any systematic shifts in their difference BE (Si 2 p)-BE (Ge 3d) as a function of alloy composition. We place an upper limit of 0.4 eV as the chemical shift to larger binding energies of the Si 2 p state between a-Si and an alloy with 80 at.% Ge. This in turn yields a maximum difference in Pauling electronegativities (X) of about 0.1. Our results therefore support the values of X obtained via thermochemical methods, and have added insight into the way other atoms will bond in amorphous alloys containing both Si and Ge.