HOLOGRAPHIC INVESTIGATIONS OF PHOTOINDUCED CHANGES IN PECVD GE-SE THIN-FILMS

The photoinduced changes in thin films of the Ge-Se system, where the ratio of Ge:Se approximate to 1:2, prepared by PECVD technology are in vestigated by holographic methods. The temporal dependence of diffract ion efficiency at constant intensify of a laser beam is investigated f or scalar and polarization recording. A typical initial maximum is obs erved, attributed to a change in transmission. The recording has ampli tude-phase character. The maximal value of the diffraction efficiency in both cases is approximately 10(-2)%. The calculations show that the photoinduced change in the refractive index \n(parallel to) - n(0)\ a pproximate to 2.10(-3). In order to induce photoanisotropy, longer exp osure is needed and \n(parallel to) - n(perpendicular to)\ approximate to 2.10(-3). The electron-microscopic analysis of the irradiated (exp osure E approximate to 250 J/cm(2)) and non-irradiated sample does not give information of a substantial change in the film topology. The re sults obtained are compared to those of films prepared by vacuum-therm al evaporation. They show that there is no substantial difference in t he value of photoinduced changes. That indicates that the medium order of the films that is associated with the method of their synthesis is not of considerable importance for the promotion of photoinduced chan ges. The results are interpreted in view of the theory of soft configu rations and defects in disordered systems. Copyright (C) 1996 Elsevier Science Ltd