Optical properties of large band gap Se- and S-doped amorphous hydrogenated silicon

Selenium- and sulfur-doped amorphous hydrogenated silicon films were prepared by the conventional plasma-enhanced chemical vapor deposition (PECVD) technique. Both Se- and S-doped films have band gaps that range from 1.7 to 2.0 eV, as a function of doping concentration. The photoresponse of the films was determined by illuminating with white light of 100 mW/cm2 intensity. The intensity variation of photoconductivity (PC) showed monomolecular recombination mechanism for a-Si:H films doped with Se (for H2Se/SiH4⩽10−1%) and S (for H2S/SiH4⩽10−2%) and bimolecular for other dopings. The persistent photoconductivity (PPC) measurements at room temperature showed that PPC increased with increasing irradiation time. PPC for Se-doped a-Si:H for a concentration of 10−3 at.% was of the same order as for 2.7×10−2 at.% S-doped sample. Photodegradation results indicate that a-Si,Se:H system would be more stable than the a-Si,S:H system as the compensation of the photodegradation due to PPC is larger in the case of Se-doped films.