The influence of laser radiation on the structure and optical properties of amorphous films in arsenic–antimony–sulphur system

Abstract

Purpose. As40 − x Sb x S60 amorphous films are suitable for creation of highly efficient, diffraction gratings, optical diffraction elements, optical compact-disks and sensors, waveguides, elements for infrared and nonlinear optics. This paper is devoted to investigation of Raman spectra of glasses and films and transmission spectra of films in As-Sb-S system with the Sb content up to 12 at % and their changes under laser radiation. Methods. Raman and optical spectroscopy, atomic forse microscopy. The transmission spectra were studied in 400-750 nm range at room temperature using a diffraction monochromator “MDR-23”. The spectral resolution was no worse than 10-3 eV. Results and discussion: Increased concentration of antimony in the composition of As40 − x Sb x S60 (0 ≤ x ≤ 12) amorphous films and laser irradiation ( λ =530 nm) of them result in the shift of their absorption edge to the longwave range. In this case the pseudogap width E g decreases, whereas the index n increases. Under the same conditions of irradiation, the largest changes in optical parameters occur in the As36Sb4S60 film. Changes in the optical characteristics of films are caused by photostructural transformations taking place in them under the laser irradiation. The nanoheterogenous structure of the studied films was established. The structural matrix of As40 − x Sb x S60 films is built from As(Sb)S3 pyramidal units connected by bridging S atoms. No molecular fragments with Sb-Sb bonds in the structure of films were detected. However, the large amount of structural groups with homopolar As-As (As4S4, As4S3) and S-S bonds (Sn) are present in the structure of films. The laser irradiation of As40 − x Sb x S60 films leads to the breaking and switching of As-As and S-S bonds in As4S4, As4S3, and Sn type structural fragments. Accompanied with the formation of structural units with heteropolar bonds As-S (AsS3). These structural transformations are related with the decreasing content of molecular fragments possessing homopolar bonds in films matrix. Conclusions. Transmission and Raman spectra of as-prepared and irradiated As40 − x Sb x S60 amorphous films were investigated. The nanoheterogenous structure of the studied films was confirmed by Raman spectra. It was established that the growth of the Sb content in composition of films and irradiation induced the absorption edge shift to the longwave region, E g decreased and n increased. The largest changed in optical parameters of as-prepared and irradiated films occur in the As36Sb4S60 film. These changes are caused by the photostructural transformations, which are accompanied by decreasing in the number of structural groups with homopolar bonds in films matrix.