Photo-assisted CVD of a-Si:H solar cells and a-SiGe:H films

High-efficiency (10%) a-Si solar cells and promising a-SiGe-H alloy films have been deposited by mercury-sensitized photochemical vapor deposition. Alloy films were prepared from mixtures of SiH/sub 4/, Si/sub 2/H/sub 6/, GeH/sub 4/, He, and H/sub 2/. The effects of gas composition and substrate temperature on film composition, H/sub 2/ bonding, and optoelectronic properties are reported. Silicon dihydride bonding is shown to decrease with increasing deposition temperature. A maximum in the ratio of dihydride to monohydride absorption peaks occurs at about 60% Ge. Preferential attachment of H to Si increases with Ge content. It is essential to minimize dihydride bonding to obtain good optoelectronic properties. Hole properties (L/sub p/ and E/sub u/) show much less dependence than electron properties (photoconductivity and conduction band tail) on Ge content for 1.4-eV films.<
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