Identification and Suppression of Si-H2 Bond Formation at P/I Interface in a-Si:H Films Deposited by SiH4 Plasma CVD∗)

Light-induced degradation is an important problem concerning hydrogenated amorphous silicon (a-Si:H)solar cells. A-Si:H films of lower Si-H₂ bond density exhibit less light-induced degradation. In this study, Raman spectroscopy measurements of a-Si:H films with P-layer/I-layer structure reveal that high-density Si-H₂ bonds exist in the I-layer within 60 nm of the P/I interface. These Si-H₂ bonds originate from surface reactions of SiH₃ radicals, as the alternative origin (i.e., cluster incorporation) is considerably suppressed by a multi-hollow discharge plasma chemical vapor deposition method. For an I-layer thickness of 20 nm, the density ratio of Si-H₂ and Si-H bonds in the I-layer decreases from 0.133 to 0.053 as the substrate temperature increases from 170◦C to 250◦C. Fine tuning of the substrate temperature during the initial stage of I-layer deposition is thus effective in suppressing Si-H₂ bond formation at the P/I interface.