A study on fast photo-response characteristics in amorphous semiconductors

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A purpose of the present study is to obtain a unified picture of fundamental physical properties in chalcogenide amorphous semiconductors. The study is mainly based on experimental results of compositional and pressure-induced effects. Photoinduced phenomena are also investigated extensively. The results obtained through the present work can be summarized as follows.First, new insights regarding the medium-range structural order have been confirmed. The structure, which can be inferred from the average coordination number Z of covalent bonding, changes from the one-dimensional chain structure to the three-dimensionally connected networks with an increase in Z from 2 to 4. Between these extrema, there exists the two-dimensional structure at around Z = 2.7.Second, a quantitative description for the mechanism of the photodarkening phenomenon has been given. The origin is ascribed to photoinduced twisting motions of chalcogen atoms. Light-intensity dependence of the photodarkening is analysed, and it is predicted that the magnitude of the photodarkening can be enhanced to twice the commonly-observed value.These two kinds of studies on the different aspects of chalcogenide glasses will be connected for investigating the photostructural transformations.