Evolution of nanostructure in hydrogenated amorphous silicon thin films with substrate temperature studied by Raman mapping, Raman scattering and spectroscopic ellipsometry

Abstract

Raman mapping and Raman scattering studies have been performed on hydrogenated silicon thin films deposited at different substrate temperature by rf-PECVD technique. In Raman mapping a clear difference in contrast, corresponding to different phases, was observed for films deposited at substrate temperature (Ts) ≥ 130 °C. The Raman spectra recorded at bright and dark spots in Raman image correspond to nanocrystalline and amorphous phase respectively. The fractional area of bright spots in Raman mapping was found to increase with increasing Ts. Also, the nanocrystalline fraction and size of nanocrystallites is found to increase with increasing Ts. These studies suggest that nucleation sites for the growth of nc-Si:H are formed at substrate temperature as low as 130 °C. With further increase in Ts more and more nucleation sites are formed which subsequently enhance crystallinity in these films. Films deposited at Ts ≥ 150 °C have larger band gap, higher roughness and higher photosensitivity and are of excellent device quality.