Amorphous films of Ge5Bi18Se77 deposited by vacuum evaporation have been studied for their thermal and optical properties. Differential scanning calorimetry (DSC) has been used to perform the thermal analysis to estimate the activation energy for crystallization (Ec) and the order of crystallization (m) of this material. The high value of (Ec), 1.672 eV, indicates good stability of the amorphous phase. The optical constants of the as-deposited, amorphous and the thermally annealed crystalline films indicate semiconducting behavior and the band gap (Eg) determined from Tauc's plot are 0.92 eV and 0.8 eV for the amorphous and crystalline films, respectively. The value of the absorption coefficient ($\alpha$) is of the order of 104cm-1 in the optical range for both amorphous and crystalline films. The studies on optical and thermal properties confirm the suitability of these firms in phase change optical recording.
Dr. T. Rajagopalan and Reddy, G. B., “Thermal and optical properties of Ge5Bi18Se77 films”, Journal of Materials Science: Materials in Electronics, vol. 11, pp. 397–400, 2000.