Device-quality polycrystalline and amorphous silicon films by hot-wire chemical vapour deposition

Abstract

Abstract We describe how high-quality intrinsic hydrogenated amorphous silicon (a-Si: H), as well as purely intrinsic single-phase hydrogenated polycrystalline silicon (poly-Si: H), can be obtained by hot-wire chemical vapour deposition (HWCVD). The deposition parameter space for these different thin-film materials has been optimized in the same hot-wire deposition chamber. A review of the earlier work shows how such high-quality films at both ends of the amorphous-crystalline scale have evolved. We incorporated both the amorphous and the polycrystalline silicon films in n-i-p solar cells and thin-film transistors (TFTs). The solar cells, with efficiencies in excess of 3%, confirm the material quality of both the a-Si: H and the poly-Si: H i-layer materials, but more work is needed to improve the interfaces with the doped layers. The TFTs made with a-Si: H and poly-Si: H channels show quite similar characteristics, such as a field-effect mobility of 0·5cm2 V−1 s−1, indicating that the channel region has amorphous-like character with a quality similar to that of state-of-the-art plasma-deposited a-Si: H TFTs. However, in contrast with plasma-deposited a-Si: H TFTs, the present HWCVD TFTs show no deterioration upon prolonged voltage bias stressing.