Study of photoconductivity and persistent photoconductivity in sulphur-doped amorphous hydrogenated silicon

We report on the spectral response and intensity dependence of photoconduct ivity (PC) and persistent photoconductivity (PPC) in plasma-enhanced chemic al vapour deposition grown sulphur-doped n-type a-Si:H films. From the inte nsity dependence of PC it is found that the addition of sulphur changes the recombination mechanism from monomolecular for intrinsic and low-doped fil ms to bimolecular at a high sulphur doping level. The photo-induced metasta ble increase of dark conductivity in these films is found to be quite simil ar to that for compensated and doping-modulated a-Si:H films. The PPC effec t is detectable up to an illumination temperature of at least 380 K the: hi ghest temperature used in this study. At 300 K the conduction persists at a level of one order higher than the equilibrium dark conductivity for over 10(3) s after removing the excitation. The PPC in a-Si, S:H is explained in terms of the valence alternation pair model.