C. Sripan

Influence of Ge addition on the optical properties of As40Se50Ge10 thin film probed by spectroscopy techniques

ABSTRACT The thin films of As40Se60 and As40Se50Ge10 were prepared on glass substrates by thermal evaporation method with thickness 1000 nm. The prepared films were amorphous in nature which was confirmed through X-ray diffraction. The chemical composition and the surface picture were obtained from energy dispersive X-ray analysis and Scanning Electron Microscopy analysis. The transmission data of the two films were collected in the wavelength range 400–1000 nm. The transmission percentage is found to be decreased whereas the absorption coefficient is increased with the Ge addition. The addition of Ge into As40Se60 is found to increase the refractive index and the extinction coefficient of As40Se50Ge10 thin film. The decrease in optical band gap is explained on the basis of increase in density of states and disorderness due to Ge addition. The optical absorption in the film is due to allowed indirect transition, and the homopolar bond density is increased with Ge addition. The Raman shift observed in the two films clearly supports the optical changes due to Ge addition.

Influence of thermal annealing on optical and structural properties change in Bi-doped Ge30Se70 thin films

ABSTRACT The effect of annealing on the structural and optical properties of thermally evaporated Ge30Se70 and Ge30Se60Bi10 thin films is reported in this paper. The prepared films were thermally annealed at 250°C to optimize the optical properties which can be used for the optical device fabrication. X-ray diffraction study revealed no structural transformation whereas the surface morphology changed as observed from scanning electron microscopy. The optical properties of the deposited and annealed films have been investigated by using a UV–VIS–NIR spectrophotometer in the wavelength range of 400–1100u2005nm. The optical band gap of the Ge30Se70 annealed film is found to be increased while the energy gap of the Bi-doped annealed Ge30Se60Bi10 thin film decreased which is explained by the chemical disorderness, defect states and density of localized states in the mobility gap. The Tauc parameter and Urbach energy which measure the degree of disorder changed with the annealing process. The transmittivity increases and the absorption power decreases in the Ge30Se70 annealed film, whereas the reverse effect is noticed for the annealed Ge30Se60Bi10 thin film. The irreversible nature of this change can be useful for optical recording purposes.

Effect of bismuth on structural and optical properties of Ge30Se70 amorphous thin film

The present paper emphasizes on the structural and optical properties change in thermally evaporated Bi doped Ge30Se70 thin film. Thin films of Ge30Se70 and Ge30Se60Bi10 were prepared by thermal evaporation technique from the bulk material under high vacuum condition. X-ray diffraction study (XRD) revealed the amorphous nature of both the films as no sharp peak was found. Scanning electron microscopy (SEM) study indicated the smooth surface for both the films. The elemental presence was confirmed from Energy Dispersive X-ray spectroscopy (EDXS). The optical transmission was recorded by Fourier Transform Infra Red (FTIR) spectroscopy in the range 500-1100 nm. The optical band gap calculated by Taucs relation shows a large decrease in band gap from 1.67 eV (Ge30Se70) to 1.05 eV (Ge30Se60Bi10) with Bi incorporation. This decrease in band gap is discussed in terms of defect states and degree of disorderness in the film. After incorporation of Bi, the increase in width of localized states in the band gap region reduces the optical band gap.