Influence of temperature on charge transports and optical parameters for the Ge15Sb5Se80 and Ge15Sb5Te80 amorphous thin films

The thin films of chemical composition Ge15Sb5Se80 and Ge15Sb5Te80 were prepared by a thermal evaporation technique. Both the absorbance and the transmittance spectra were measured over the incident photon energy ranges 1.14 to 2.7 and 1.22 to 2.87 eV for the Ge15Sb5Se80 and Ge15Sb5Te80 films respectively. These were used for estimating the reflectance spectra in the same range of the incident photon energy. Both the measured and estimated spectra were carried out in the temperature range 250 to 330 K. With the aids of these spectra, the temperature dependence of charge transports and optical parameters were investigated and analyzed. Using the reflectance spectra, the refractive indices for the Ge15Sb5Se80 and Ge15Sb5Te80 films were determined in the low energy region of the studied incident photon energy range. These refractive index values were plotted as a function of the long wavelengths for the completely investigated range of temperature. These plots were used for elucidating the temperature dependence of both the oscillator and dispersion energies of the refractive index in the Ge15Sb5Se80 and Ge15Sb5Te80 thin films. Thereafter, static refractive index and static dielectric constant were determined. Also the temperature coefficients of the optical band width were determined and discussed for the two mentioned films.