Photoacoustic and xerographic investigation of the gap-state structure ofa−Se: Comparison witha−Si:H

The first application of the photoacoustic-spectroscopy (PAS) technique to chalcogenide thin films is reported. The PAS-derived value for the mid-gap density of states for $a-\mathrm{S}\mathrm{e}$, 1 × ${10}^{15}$ ${\mathrm{cm}}^{-3\mathrm{}}$, is found to be in good agreement with xerographic measurements. These results for $a-\mathrm{S}\mathrm{e}$ are contrasted with PAS data for a series of $a-\mathrm{S}\mathrm{i}:\mathrm{H}$ films made by ion-beam deposition. The PAS defect population for the $a-\mathrm{S}\mathrm{i}:\mathrm{H}$ network semiconductor is shown to be highly compositionally dependent with two identifiable hydrogenation regimes.