Compositional dependence of the photoinduced phenomena in thin chalcogenide films

The results presented in this paper concern the changes in transmittance, reflectance, refractive index and band-gap in the visible and NIR region, transmissivity in the IR, dissolution rate in alkaline solutions and dry etching rate of some As- and Ge-containing chalcogenide thin films depending on composition and conditions of their deposition. and exposure to light, It was found that the: method of evaporation influences considerably the properties of thin chalcogenide films. The addition of Bi and Tl in As2S3 and GeS2 leads to shifting of the absorption edge to the longer wavelengths. Using TRRm methods (R-m is the reflection of 100 nm thick films deposited on Si substrate), the thickness of very thin layers from the systems As-S, GeS2 and Ge-S-As have been determined with an accuracy of +/-2 nm and for determination of the refractive index it was less than +/-0.005, The data from the transmission measurements were compared with those from the ellipsometry. The great importance of evaporation temperature, film composition and pH of the solutions for achieving maximum change in the dissolution rate of the layers has been shown. It has been concluded that the irreversible changes resulting from illumination of as-deposited As-S films are connected with photo-induced transformation of the As-As and S-S bonds into As-S ones and subsequent polymerization of As4S4 molecules. The photo-induced changes in the ternary systems could be explained by the creation of new states in the band gap of the systems. These changes allow the practical application of thin-layered information recording media and high-resolution inorganic photoresists.