Photodarkening In insitu Textured PbTe Eilms - A Novel Technique for High Contrast Optical Storage in Polycrystalline Thin Eilms

Recent studies (1,2) have shown that textured films are ideally suited for optical storage as they exhibit appreciable optical contrast upon laser irradiation. Craighead et al (1) demonstrated that relatively thick films of various materials exhibit good reflectance contrast due to a mechanism of columnar collapse, when the films are prepared by sputter-etch technique. Kameswara Rao et al (2) observed that thin films of Ge, prepared by oblique angle deposition technique, exhibit good transmittance contrast due to chemical modification of the irradiated region to a selective oxide phase. It thus appears that the origin as well as the nature of the optical contrast in textured films critically vary with method of preparation as well as the thickness of the film. In the present study we report the observation of optical contrast of thin polycrystalline films of PbTe, via darkening of irradiated region. The observed darkening is found to be similar to the photodarkening widely known in amorphous materials.