Structure and photoinduced changes in bulk and films of As–Ge–S system

Abstract

Structure and basic physico-chemical properties of the bulk samples and vacuum evaporated thin films of AsxGe40−xS60 (x=0, 10, 20, 30, 40) were studied in this work. The Raman spectra showed that the structure of bulk samples as well as the films consists of AsS3/2 and/or GeS4/2 basic units, and other units containing homopolar bonds (As–As and/or Ge–Ge and S–S). The concentration of homopolar bonds in the as-prepared thin layers is higher than that in the bulk samples of the same composition. Exposure to halogen light decreases the concentration of these homopolar bonds as the structure of films approaches that of the bulk samples. Considerable changes in optical properties of films such as optical transmission, refractive index and chemical resistance accompany this light-induced chemical homogenization. These glasses have a broad window of high IR transmissivity (≈70%) up to λ=10–11 μm. In the IR spectrum of binary Ge40S60, intensive absorption bands appear, which indicate partial hydrolysis of the sample. In contrast to bulk samples, the films are photosensitive. Exposure to halogen lamp light causes both photodarkening and photobleaching of thin films depending on the Ge content, with corresponding decrease and/or increase of refractive index in the visible and near IR regions. The addition of Ge into the films of As–S system can eliminate or alter the character of photoinduced changes of optical parameters.