Nanostructured Ge distribution in a-SiGe: H alloys from anomalous small-angle X-ray scattering studies

The nanostructures of hydrogenated amorphous silicon germanium alloys, a-Si(1 - x)Ge(x):H (x similar to 0.5 to 0.7), prepared by different plasma enhanced chemical vapor deposition techniques, are examined by anomalous small-angle X-ray scattering (ASAXS). Clear evidence of inhomogeneous distributions of Ge are found with correlation lengths of 1.0 to 1.4 nn. This non-uniformity is removed by enhanced ion bombardment during growth and it is reduced by hydrogen dilution of the plasma. These more homogeneous materials result in improved photovoltaic and opto-electronic performance. The anisotropic ASAXS from the Ge is consistent with Ge enrichment along columnar-like nanostructures. (C) 1998 Elsevier Science Ltd. All rights reserved.