Influence of atomic hydrogen on the growth kinetics of a-Si : H films and on the properties of silicon substrates

We present two different investigations showing the influence of hydrogen i n hot-wire chemical vapor deposition (HWCVD). First, dissimilarities in the growth kinetics of hydrogenated amorphous silicon (a-Si:H) films by the pl asma enhanced chemical vapor deposition (PECVD) and HWCVD are discussed. A series of a-Si:H films with varying substrate temperature (T,) was deposite d by HWCVD and PECVD. In comparing the initial growth, which was measured b y in-situ kinetic ellipsometry for both deposition methods, we conclude tha t, in the PECVD process, a faster coalescence takes place as a result of a larger surface mobility of the adsorbed precursor radicals at the growing s urface. This dissimilarity can be explained by different silane dissociatio n processes which yield to a higher ratio of atomic hydrogen to silicon rad icals and a lower hydrogen coverage of the film growing surface in the case of HWCVD. Therefore, dense high quality a-Si:H films deposited by HWCVD ar e formed at higher substrate temperatures and lower hydrogen dilutions comp ared to PECVD. The second investigation deals with the effect of atomic hyd rogen on polished and textured silicon wafers. The hydrogen treatment can d ecrease the surface defect density without deteriorating the properties of the bulk material. Therefore, the fill factor and the open circuit voltage of (n)a-Si:H/(p)c-Si heterojunction solar cells increase and the intrinsic conversion efficiency reaches up to 15.2%. (C) 2001 Elsevier Science B.V. A ll rights reserved.