THERMODYNAMIC MODELING OF THE LOCAL ATOMIC ORDER IN AMORPHOUS-ALLOYS BASED ON SILICON AND GERMANIUM

The free-energy model (FEM) previously developed for the prediction of the bonding in amorphous covalent alloys is applied here to amorphous alloys based on Si and Ge. Predictions of the FEM are presented which indicate that H is preferentially bonded to Si and that dangling bonds appear preferentially on Ge atoms in amorphous Si(x)Ge(y)H(z) (a-Si(x)Ge(y)H(z)) alloys, thus demonstrating that these experimentally observed effects need not be attributed to specific deposition conditions. In addition, it is predicted that 0 bonds preferentially to Si in a-Si(x)Ge(y)O(z) alloys and that Ge will be more strongly oxidized when present in very dilute concentrations in a-SiO2.