THE EFFECT OF PREPARATION CONDITIONS ON THE MORPHOLOGY OF LOW-TEMPERATURE SILICON FILMS

The structure of UHV-evaporated a-Si and reactively-evaporated a-Si:H films, as observed by TEM, is correlated with preparation conditions. The results suggest that a-Si growth by various vapor-deposition techniques can be interpreted in terms of the effect of the deposition parameters on nucleation and coalescence. UHV-evaporated films contain a large volume fraction of surface-life tissue. Higher substrate temperatures enhance agglomeration, resulting in a two-phase structure consisting of island clusters interconnected by a porous amorphous tissue. 'Activated' hydrogen increases the nucleation density, resulting in a more homogeneous fine-grained structure, while silicon hydrides further enhance coalescence between the island structures. The application of a positive substrate bias during film growth promotes microcrystallite formation in both a-Si and a-Si:H films.