Structural, optical and electrical characterization of amorphous Se xTe 1− x thin film alloys

Abstract

The structure, the optical and photoelectric properties of amorphous Se x Te 1− x thin film alloys prepared by thermal evaporation, were analyzed using Raman spectroscopy, optical transmission and two-point probe photoconductivity measurements. The composition, x, was varied in the range of 0.32–1. The Raman measurements indicate an amorphous structure for all compositions. The Raman peaks are assigned to vibrations of the Te–Te, Te–Se and Se–Se pairs. This assignment is confirmed by a quantitative analysis of the integrated peak intensity vs. composition. Using optical transmission and reflectivity measurements, the optical band gap ( E g) and the optical constants (refractive index and extinction coefficient) were found for all compositions in the red and near-infrared part of the spectrum. It is found that the E g value increases linearly with ‘ x’, from about 1 eV for x=0.32 to 1.88 eV for x=1, whereas the photoconductivity increases exponentially with x, changing its value by more than three orders of magnitude. The latter is explained in terms of variation in the lifetime of charge carriers, which depends on the sample composition.