As-grown defect concentrations in undoped amorphous hydrogenated material which had been deposited by means of radio-frequency glow discharge were investigated. It was found that the defect density behaved in a similar manner to the concentration of SiH2 configurations in films which had been deposited at substrate temperatures below 300C. The defect concentration was proportional to the third or fourth power of the SiH2 concentration; depending upon the deposition conditions. The Urbach energy increased in samples which had been deposited under conditions where the SiH2 concentration increased. It was found that an additional energy was required in order to convert weak bonds, in the valence-band tail, into defects. The observed characteristics were analyzed by using a model in which this additional energy was produced by a surface reaction of SiH3 which incorporated the SiH2 configuration into the network. These characteristics were compared with those of the Staebler-Wronski effect. It was noted that the increase in weak-bond density contributed to an increase in defect creation efficiency. There were similarities in the mechanisms for as-deposited defect formation and for the Staebler-Wronski effect.

K.Maeda, I.Umezu, H.Ishizuka: Physical Review B, 1997, 55[7], 4323-31