Method for Deriving the Complex Infrared Dielectric Function of Amorphous Thin Films from Infrared Reflectivity Spectroscopy

Abstract

Although advanced nonlinear optical techniques have demonstrated high potential for examining elementary excitations in semiconductors, infrared reflectivity analysis remains the most quantitative technique because simple theories can be used to describe the material response to an infrared wavelength excitation. Line shape analysis, comparatively rare for non-linear optical spectroscopy, can be carried out to yield quantitative results. Therefore, our objective in the present thesis is to develop an experimental approach based on infrared spectroscopy for the characterization of the complex infrared dielectric function of amorphous thin films grown on a substrate, which is inaccessible by other means. The proposed approach is based on the analysis of the infrared reflectivity spectrum of the considered film/substrate using a numerical technique combining the Fresnel theory and the Kramers-Kronig conversion theorem. We used the technique developed to deduce the complex infrared dielectric function of amorphous silicon carbide thin films deposited on silicon at different temperatures and pressure levels using the pulsed laser deposition (PLD) growth technique. The results obtained showed that the growth temperature does not have a significant effect on the dielectric properties of the amorphous films. However, the variation in pressure allows a substantial modification of the real and imaginary parts of the infrared complex dielectric function of the amorphous silicon carbide film. We believe that the optical technique developed in this work constitutes a non-destructive method for the characterization of relevant infrared properties of amorphous materials, which so far are not clear to materials scientists.