BULK AND SURFACE DENSITIES OF STATES OF 0.3-MU-M-THICK HYDROGENATED AMORPHOUS-SILICON FILMS USING PHOTOTHERMAL DEFLECTION SPECTROSCOPY

An analysis of the absorption spectra, distorted by an interference ef fect in 0.3-mu m-thick hydrogenated amorphous-silicon (a-Si:H) films, is carried out. In the midgap region, the absorptance interferograms, as measured by photothermal deflection spectroscopy, reveal that a-Si: H films have a 10-30-nm-thick surface-defective layer, whereas silicon nitride covered films show a more uniform defect profile. Unlike the bulk layer, the surface density of states is independent of light soak ing and thermal annealing, and has a similar absorption spectrum to do ped a-Si:H films.