Study on structural fluctuations in amorphous semiconductors by micro-light scattering

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While long-range order is lacked in amorphous semiconductors, short-range order such as bond-length and bond-angles are conserved. Between the two scale of order, the medium-range order in a few 10 nm scale is important. For example, photo-induced crystallization of amorphous materials does not occur immediately at the irradiation, but it proceed after some ratent period under the irradiation. Perhaps some ordering states are developed during the ratent period, and there are large fluctuations in the amorphous states. The aim of this research is to clarify local character of amorhous semiconductors, such as the medium-range fluctuations, and fractal structures in the photo-induced crystallization process. In this year experimental setup has been made, and the measurement has been done preliminarly. As the result, it is difficult to observe amorphous fluctuations by Leyrey-scattering using micro-optics. One reason may be that the relating electronic state is spread wider than spacial range of fluctuations. We have rearranged the optical system for Raman scattering measurement with a liquid He cryostat to study the network vibrations in the amorphous states at low temperatures.