Electron spin resonance study of hydrogenated microcrystalline silicon-germanium alloy thin films

摘要

Paramagnetic defects of undoped hydrogenated microcrystalline silicon-germanium alloys (mu c-Si1-xGex:H) grown by low temperature (200 degrees C) plasma-enhanced chemical vapor desposition (PECVD) have been measured by electron spin resonance (ESR) and compared with those of hydrogenated amorphous silicon-germanium (a-Si1-xGex:H). The spin density of mu c-Si1-xGex:H increases with Ge content and shows a broad maximum of similar to 10(17) cm(-3) at x similar to 0.5, which reasonably accounts for the decreased photoconductivity. While the Ge dangling bond defects prevail in a-Si1-xGex:H for Ge-rich compositions, we detected no ESR signal in mu c-Si1-xGex:H for x > 0.75 where an electrical change occurs from weak n- to strong p-type conduction. These results indicate that dangling bonds are charged in large densities due to the presence of the acceptor-like states in undoped mu c-Si1-xGex:H.