CORRELATION BETWEEN OPTICAL DEFECT DENSITY AND SPIN DENSITY IN AMORPHOUS SILICON CARBIDE

Abstract

Amorphous silicon carbide (a-SiC:H) films deposited by different techniques under different deposition conditions have been submitted to photo-thermal deflection and photoacoustic spectroscopy (PDS and PAS) and electron spin resonance (ESR) measurements in order to obtain, through the trend of low energy absorption coefficient and the density of spins, information on the nature, energy and number of defects. The results obtained from the two techniques are often in disagreement since the dangling bond density generally does not scale with the integrated defect density. In order to explain the discrepancy the absorption coefficient has been calculated, following the Tauc model, in the three regions of fundamental absorption, Urbach tail and excess absorption. An expression for the density of defects has been obtained which depends on the integrated excess absorption coefficient through a proportionality factor.