The effect of hydrogen dilution on the microstructure and stability of a-Si:H films prepared by different techniques

In this study, we present in situ kinetic and spectroscopic ellipsometry investigations concerning the growth and microstructure of hydrogen (H)-diluted hot-wire (HW) deposited amorphous hydrogenated silicon (a-Si:H). A comparison of the results obtained for HW-films with those for films prepared by the conventional plasma enhanced chemical vapour deposition (PECVD) reveals that II-dilution has a completely different effect in both cases. While the density of PECVD material increases with increasing dilution ratio, the opposite behaviour is measured for the HW-material. In agreement with our earlier results obtained for amorphous hydrogenated thin films deposited in pure silane which directly relate the stability of these films to the corresponding microstructure (density, surface roughness and hydrogen bonding configuration), we explain the decrease in stability of the II-diluted HW-films with increasing dilution ratio by an appropriate change in film growth and the resulting microstructure. (C) 1998 Elsevier Science B.V. All rights reserved.