Photo Structural Phase Transitions in Amorphous Chalcogenides:Basic Principles and Applications in Holography and Optical Information Processing

Abstract

Since their discovery in the mid 50th by Kolomiets and Goryunova amorphous chalcogenides have gained an increasing attention during the last decades [1]. They exist with widely varying stoichiometry in binary AxB1-x and more complex compounds. Due to their common layered structure amorphous chalcogenides are known as Se-like systems. They can be produced by cooling molten solids (bulk glasses) or thermal evaporation (thin films). The degree of disorder determined by the medium range structure is higher in thin films than in bulk glasses. Most of the amorphous chalcogenide semiconductors show photoinduced phase transitions and thermal annealing. Therefore, three states are distinguished. The freshly quenched or evaporated, the annealed and the photodarkened state. The photosensitivity and the photoinduced changes of the optical parameters like the refractive index etc. are about one order of magnitude larger for the fresh state than the annealed one. Nevertheless annealed materials and the reversal photodarkening are better investigated due to the greater determination of the annealed state and the independence of different production parameters. Scientists from all over the world used many different methods to learn more about the attractive photostructural phase transitions in amorphous chalcogenides. Treacy et al. used nuclear quadrupole resonance to detect certain molecular units in thin films and bulk glasses of As2S3 and As2Se3 [2]. Raman-spectroscopy was employed by Fumar et al. [3]. At the University of Raleigh, North Carolina, the dependence of reversal photodarkening on the intermediate range order were investigated by means of several x-ray scattering experiments [4-7]. Elliot used related methods to get more