Effect of illumination on hydrogenated amorphous silicon thin films doped with chalcogens

Hydrogenated amorphous silicon thin films doped with chalcogens (Se or S) were prepared by the decomposition of silane (SiH4) and H2Se/H2S gas mixtures in an RF plasma glow discharge on 7059 corning glass at a substrate temperature 230 °C. The illumination measurements were performed on these samples as a function of doping concentration, temperature and optical density. The activation energy varied with doping concentration and is higher in Se-doped than S-doped a-Si:H thin films due to a low defect density. From intensity versus photoconductivity data, it is observed that the addition of Se and S changes the recombination mechanism from monomolecular at low doping concentration films to bimolecular at higher doping levels. The photosensitivity (σph/σd) of a-Si, Se:H thin films decreases as the gas ratio H2Se/SiH4 increased from 10−4 to 10−1, while the photosensitivity of a-Si, S:H thin films increases as the gas ratio H2S/SiH4 increased from 6.8 × 10−7 to 1.0×10−4.