Density of gap states in a-SiC:H films by means of photoconductive and photothermal spectroscopies

Abstract

In the present work we report and discuss results on the gap density of states for a-SiC:H films, deposited by PECVD with different CH 4 flow rates, through the deconvolution of CPM and PDS spectra. The occupied density of states in the gap is in first approximation the derivative of the CPM spectrum with respect to the photon energy. Below the Urbach edge the PDS and CPM techniques are sensitive to different electronic transitions. From the difference between PDS and CPM spectra the deep unoccupied density of defects above the Fermi level can be deduced. This procedure has been applied for the first time to the a-SiC:H binary alloy. We have obtained that the defect distribution ascribed to silicon dangling bonds can be fitted by gaussian curves with increasing correlation energy and halfwidths as the carbon content increases.