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

Selenium- and sulfur-doped amorphous hydrogenated silicon films were prepar ed by the conventional plasma-enhanced chemical vapor deposition (PECVD) te chnique. 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 film s was determined by illuminating with white light of 100 mW/cm(2) intensity . The intensity variation of photoconductivity (PC) showed monomolecular re combination mechanism for a-Si:H films doped with Se (for H2Se/SiH4 less th an or equal to 10(-1)%) and S (for H2S/SiH4 less than or equal to 10(-2)%) and bimolecular for other dopings. The persistent photoconductivity (PPC) m easurements at room temperature showed that PPC increased with increasing i rradiation time. PPC for Se-doped a-Si:H for a concentration of 10(-3) at.% was of the same order as for 2.7 x 10(-2) at.% S-doped sample. Photodegrad ation 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 l arger in the case of Se-doped films. (C) 2000 Elsevier Science B.V. All rig hts reserved.