水素化アモルファスシリコンの光劣化と光誘起構造変化(<特集>半導体エレクトロニクス)

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Reversible photo-induced change has been observed in the polarization dependence of transverse electroabsorption signal in hydrogenated amorphous silicon (a-Si : H), which is indicative of structural change occurred in the whole material. The structural change in a-Si : H saturates in a few minutes upon light exposure, which is a short time in comparison with the saturation time of photoconductivity degradation and more than 10 hours' annealing is necessary for restoring to initial state. Accounting for the results of various investigations, photo-induced structural change may occur through the following processes : (1) The structural disorder increases with light exposure and is observed as a PEA. In particular regions, the local network distortion becomes significant and causes surround network to distort. The strained region enlarges by creating metastable strained bonds. (2) Bond breaking is caused by the collision of such a strained region with another such region. Since the region of intersection will be the most highly strained region. (3) The produced dangling bond pair move through such a bond switching process to reduce strain energy. (4) The PEA ratio saturates when the strained regions cover almost the whole volume. However the density and internal stress will not saturate until they reach a averaged state of distortion distributed throughout the material. Therefore the time to reach the averaged state is considered to depend on the light exposure history. Because the size and distribution of strained region may depend on their consecutive growth time. The breaking process continues with collisions of the strained region in smaller and smaller un-affected parts of the material. On the other hand, in annealing process, the structural restoration begins with the most highly strained regions which is located to near the dangling bond defects.
2001-04-15

水素化アモルファスシリコンの光劣化と光誘起構造変化(<特集>半導体エレクトロニクス)

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