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

Paramagnetic defects of undoped hydrogenated microcrystalline silicon–germanium alloys (μc-Si1−xGex:H) grown by low temperature (200 °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 μc-Si1−xGex:H increases with Ge content and shows a broad maximum of ∼1017 cm−3 at x ∼ 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 μc-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 μc-Si1−xGex:H.