Optical properties of μc-Si:H/α-Si:H layered structures: Influence of the hydrogen bonds, crystallite size, and thickness

Abstract

Thin films of layered μc‐Si:H/α‐Si:H structures grown with rf magnetron sputtering have been studied with spectroscopic ellipsometry (SE) and Raman spectroscopy (RS). Analysis of the dielectric function spectra with the Si‐centered tetrahedron model and deconvolution of the Raman spectra suggest that the silicon‐hydrogen bonds are correlated with the microscopic voids in α‐Si:H while the good quality α‐Si:H films exhibit SiH₃ bonds and small amount of SiH₂ bonds. The quality of the surface and interface of the μc‐Si:H/α‐Si:H was analyzed by SE and transmission electron microscopy and the dependence of an interfacial amorphous layer at the initial stages of the μc‐Si:H growth on the argon and hydrogen pressure was found. Furthermore, a correlation between the SE and RS results on μc‐Si:H layers is shown and commented, while a dependence of the energy shift and the broadening of the interband transitions and the Raman transverse optical peak on the mean crystallite size has been found and discussed in view of the finite size and stress effects on the electronic structure of these materials. This analysis suggests that strain is one of the most important factors during the growth of μc‐Si:H.