Characterization and control of crystal nucleation in amorphous electron beam evaporated silicon for thin film solar cells

The kinetics of crystal nucleation in high rate electron beam evaporated amorphous Si for polycrystalline thin film solar cells was systematically studied on SiN and selected ZnO Al coated glass substrates with dissimilar surface topographies by employing Raman spectroscopy, transmission electron microscopy and optical microscopy. The influence of the surface topography of the substrate and the disorder of the deposited amorphous Si could be correlated to the respective characteristics of the transient and steady state regime of the nucleation rate. The steady state nucleation rate Iss, its corresponding activation energy EIss and consequently the size of the grains in the crystallized Si were found to be governed by the interplay between the surface roughness and the deposition temperature. The steady state nucleation rate Iss increased gradually upon increasing the substrate roughness, while lowering the deposition temperature of the amorphous Si on rough textures resulted in a decline of Iss. The time lag amp; 964;, which represents a distinctive parameter for the transient regime, was only slightly affected by the substrate topography. The deposition temperature, however, had a significant influence on amp; 964;, with amp; 964; increasing by a factor of 8 upon lowering the deposition temperature from 300 to 200 C for all substrate topographies. These characteristics could be correlated with the increasing structural disorder of the deposited a Si upon decreasing the deposition temperature. Based on this analysis, we could determine design rules for the controlled preparation of large grained poly Si in minimized processing time on any of the used substrate types, by individually adjusting the deposition temperature and implementing nucleation layer