Microstructural analysis of nanostructured amorphous silicon-germanium alloys: Numerical modeling

A detailed microstructural analysis of amorphous silicon-germanium alloys with germanium fraction ranging from 0.1 to 0.5 is performed by means of a numerical modeling technique. By substituting Ge atoms for Si atoms in nanoporous paracrystalline network of amorphous silicon, several amorphous silicon-germanium structures have been generated then relaxed. The main aim of our work is to study the effect of compositional heterogeneities on the structural properties of amorphous silicon-germanium alloys in comparison with the standard case, that of a homogeneous random distribution of the atoms. In the present work we envisage the two-phase amorphous silicon-germanium model proposed by Goerigk and Williamson to interpret their anomalous small-angle X-ray scattering measurements; it consists on a mixture of Ge-rich and Ge-poor domains at the nanoscale. The microstructure of our structural models is analyzed by examining the macroscopic mass density, the X-ray diffraction intensity, the radial distribution functions, the bond lengths and the coordination numbers within the first coordination shell of Si and Ge atoms.