Spectroscopic ellipsometry analysis of amorphous silicon thin films for Si-nanocrystals

Hydrogenated amorphous and nano-crocrystalline silicon thin films were grown by very-high-frequency plasma-enhanced chemical vapor deposition (VHF-PECVD, 60 MHz). In this paper, we report the defects of nano-crystallites embedded in an amorphous matrix of hydrogenated silicon alloy (a-Si:H) thin film as investigated by spectroscopic ellipsometry (SE). The peak intensity and position of the imaginary part of the dielectric constant (epsilon2) as a function of the energy show various material states, including a-Si:H (3.5 eV) and nc-Si (4.2 eV), along with the absorption coefficient, thickness, optical gap, and the characteristics of the defects. The ratio of the characteristic Raman features, the TA/LO and LA/LO ratio, is related to the defect states in the films. It was correlated to the SE data. Following this, we look into the systematic change in the crystallinity of the film from the SE results. Quantized crystallinity values from the SE data show good agreement by more than 88.75% with the crystallinity information obtained through Raman spectroscopy.