A physicochemical interpretation of the photoconductivity of a-Si : H

2014 Total hydrogen content and its distribution among SiH, SiH2 and other H’ sites of sputtered a-Si : H films vary after posthydrogenation but the dangling bond concentrations remain constant. This can be explained by preferential H diffusion in the tissue zone where most of the hydrogen is located, while the residual dangling bonds are in the islands. The photoconductivity is controlled by spinless defects of the tissue zone originating from back defects of H on their various sites. It decreases as the relative SiH2 content increases. J. Physiaue LETTRES 44 (1983) L-265 L-269 ler AVRIL 1983, Classification Physics Abstracts 73.60F 81.40 72.40 The localized states in sputtered a-Si : H can be introduced by Si « structural » defects either connected only to the disorder in the Si atom positions (pure Si matrix defects) or connected with one or several hydrogen sites (H related defects) [1]. It is important to distinguish between them before making further attempts to decrease their density. Systematic variations of the deposition conditions change continuously the concentration and the nature of both pure Si matrix defects and H related defects [2]. However, posthydrogenation [3] drastically changes the concentration of H on its various sites. There is now more and more evidence that a-Si : H is an inhomogeneous material [4] with two parts less disordered islands embedded in a more disordered connective tissue. In this case, the photoconductivity might be controlled predominantly by one part of the film, as other properties are [5]. From NMR measurements, most of the hydrogen stays in the more disordered connective tissue, while [H] concentration in the island is weak ( N 3 %) and rather independent of the preparation conditions [4]. From the comparison of the photoconductivity before and after posthydrogenation, which changes strongly the structure of the tissue, we can check whether the photoconductivity is strongly sensitive to this part of the film or not.