EXPERIMENTAL-EVIDENCE OF PHOTOINDUCED EXPANSION IN HYDROGENATED AMORPHOUS-SILICON USING BENDING DETECTED OPTICAL-LEVER METHOD

Photoinduced structural change in hydrogenated amorphous silicon (a-Si :H) has been studied by a sensitive bending detection method using an optical lever. We observed that a-Si:H films show not only thermal exp ansion due to a photothermal effect but also residual and persistent e xpansion after light soaking. The volume change is recovered by therma l annealing at 200 degrees C. A dehydrogenated sample annealed at 550 degrees C and a microcrystalline sample, in which photoinduced defects are not created, show little photoinduced expansion. The photoinduced expansion and photoinduced defect density show identical time evoluti on. These results suggest that the photoinduced expansion is related t o the photoinduced defect creation. A quantitative evaluation of the p hotoinduced expansion indicates that the photoinduced structural chang e is spread over several molecular volumes around a photocreated defec t. (C) 1998 American Institute of Physics.