AN INSITU ELLIPSOMETRY STUDY OF AMORPHOUS-SILICON AMORPHOUS-GERMANIUM MULTILAYERS

We present an in-situ ellipsometric study of hydrogenated amorphous silicon (a-Si:H)/hydrogenated amorphous germanium (a-Ge:H) multilayer structures. We deposit multilayers structures with the thickness of the Si layer equal to that of the Ge layer and with thicknesses of 100 and 500 angstrom. We find that whereas the a-Ge:H grown on top of a-Si:H follows a uniform growth model, the initial stage of growth of a-Si:H on a-Ge:H must be modelled with a hemispherical nucleation model. These growth mechanisms are observed for both the case of the 100 angstrom layers and the 500 angstrom layers. We also find that there are no long-term effects of the deposition on the optical properties of the layers. This is observable visually in the cases where the thickness of the layers allow the real-time trajectories to reach a saturated value and thus guaranteeing the same starting ellipsometric point for the next layer. This assures us that each material at the beginning of the superlattice growth is the same as the grown at the end. The implication of the present analysis on quantum size effects of superlattices is discussed.