Spectral and Morphological Studies of Nanocrystalline Silicon Thin Films Synthesized by PECVD for Solar Cells

摘要

In this work, a series of nanocrystalline silicon films were studied with different microstructural tools to elucidate the film microstructure at different stages of growth. Thin Si films, with a series of multilayers, were deposited by radio frequency glow discharge using Plasma Enhanced Chemical Vapour Deposition (PECVD) in silane gas (SiH₄) highly diluted by hydrogen. Different nanostructured films were prepared by systematically varying gas flow ratios (R = 1/1, 1/5, 1/7.5, 1/10, 1/15, 1/20) for films having different thicknesses. By changing the structure of the material, going from pure amorphous to nanocrystalline silicon, it is possible to obtain a variation in optical gap using the same material. In these structures, layers with different individual optical gaps are stacked together in order to cover as much of the solar spectrum as possible. The nanostructures of the silicon thin films were studied using FTIR, RS, PL, XRD, AFM, SEM, TEM and HRTEM. The results were correlated for conglomerate surface, grain surface. Some theoretical calculations were used for designing the overall stack geometry and for interpretation of characterization. These agree well with experimental observation.