In-gap optical absorption of amorphous Si3N4

Abstract

The optical absorption coefficient of thin films of chemically vapor deposited amorphous Si3N4 has been measured for photon energies ranging from 1.7 to 3.9 eV using photothermal deflection spectroscopy. From these data it can be inferred that these films contain between 10 and 100 ppm in-gap electronic states, a number consistent with estimates of the trapped charge density in metal-nitride-oxide-semiconductor devices. While other investigators have inferred the existence of well defined trap energies from electrical data, the present measurements yield only broad, rather featureless absorption spectra.