Annealing Effects on Structural and Optical Properties of Ge10Sb30Se60 Thin Film

The optical constants of as-prepared and thermally annealed Ge10Sb30Se60thin films were determined. Effect of heat treatment on the structure and optical properties of Ge10Sb30Se60 thin films in the range between the glass transition and crystallization temperature have been investigated. The glass transition and crystallization temperature of the synthesized sample was measured by non- isothermal DSC measurements. The microstructure and optical properties of these films were characterized by UV-VIS spectrum, scanning electron microscope (SEM) and X-ray diffraction (XRD). The optical band gap for as-prepared and annealed films have been calculated using Taucs low from the optical transmission and reflection spectra. The results indicate that the optical band gap Eopt increases when the annealing temperature (Ta) is lower than the glass transition temperature (Tg), while decreases with further increase of Ta. The XRD studies show that the as-prepared film is amorphous in nature, but the crystalline improved with increasing the annealing temperature. Furthermore the particle size and crystalline increases while the dislocation and strains decreases with increasing the annealing temperature. Thermal annealing was found to be accompanied by structural effects, which in turn, lead to change in the optical constants. The obtained results were explained in terms of the Mott and Davis model for amorphous materials and amorphous to crystalline structure transformations

Determination of Optical Band Gap and Optical Constants of GexSb40-xSe60 Thin Films

GexSb40-xSe60 (where 10≤ x≤ 30 at %) thin films were prepared on glass substrates by thermal evaporation technique. X-ray diffraction analysis for as – deposited films showed that they have amorphous structure. The optical constants of the as- deposited films were calculated from optical transmittance and reflectance data in wavelength range from 400 to1200 nm. We found that both refractive index, n and extinction coefficient, k increased with increasing photon energy. Optical band gap was determined from absorption coefficient data using Tauc procedure and from the energetic distribution of the absorption coefficient. The optical absorption data indicate that the absorption mechanism is due to indirect transition. The optical gap of the as- deposited films was found to decrease monotonically with increasing Sb content , a result was interpreted on the basis of the chemical- bond approach. The dispersion of the refractive index is analyzed in terms of Wemple- DiDomenico single oscillator model. The optical dispersion parameters E0 and Ed were determined according to this model. The characteristic Urbachs parameters such as steepness parameter, σ and Urbachs energy have been determined. The real and imaginary parts of the dielectric constant in addition to the dissipation factor tan δ and the optical conductivity were also determined

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