Infrared insight into the network of hydrogenated amorphous and polycrystalline silicon thin films

Abstract

IR measurements were carried out on both amorphous and polycrystalline silicon samples deposited by PECVD on glass substrate. The transition from amorphous to polycrystalline phase was achieved by increasing dilution of silane plasma at the deposition process. The samples were found to be mixed phase materials. Commonly, infrared spectra of hydrogenated silicon thin films yield information about microstructure, hydrogen content and hydrogen bonding to silicon. In this paper, additional understanding was retrieved from infrared response. Applying standard optical laws, effective media theory and Clausius-Mossoti approach concerning the Si-Si and Si-H bonds under IR irradiation as individual oscillators, refractive indices in the long wavelength limit, crystalline, amorphous and voids volume fractions and the mass density of the films were determined. The mass density was found to decrease with increasing crystalline volume fraction, which can be attributed to the void-dominated mechanism of network formation.