Study the Effect of Ga content on the physical properties of thermally evaporated (Ge25-xGax Se75) thin films

Abstract

Ge25-xGaxSe75 bulk ingot materials with 5.97 ≤ x ≤ 23.95 were prepared by direct fusion of stoichiometric proportions of the constituent high purity elements in vacuum saled-silica tubes, following controlled heating and cooling stages. X-ray powder diffraction patterns indicates that for different values of x the materials corresponding to hexagonal phase is presented. Nearly stoichiometric films with different x values were prepared by conventional thermal evaporation technique using molybdenium boats in 10-4 Pa with a deposition rate 1.8 nm/sec on optically flat glass substrates at 300 K. X-ray, transmission electron microscopy, electron diffraction, scanning electron microscopy and energy dispersive X-ray spectrometer were emplying to characterize the deposited films. The effect of annealing temperature in vacuum on the microstructure of the deposited films were investigated. The optical properties of the deposited Ge25-xGaxSe75 thin films were calculated in the wavelength range 500-2500 nm. The refractive index of the deposited films was found to follow the two-term Cauchy dispersion relation. The dispersion of the refractive index data could be described according to the simgle osallator model, from which the oscillator parameters as well as other optical parameters were calculated. The electric free carrier susceptibility and the values of the carrier concentration to the effective mass ratio were calculated. Graphical representation of the surface and volume energy losses function were also presented. The absorption coefficient of Ge25-xGaxSe75 thin films with different values of x was analysed and the optical band gap was calculated. The DC and AC electical conductivity of the deposited films were studied. The DC electrical conductivity revealed that, two conduction mechanisms were observed in the temperature range 300-470 K. The activation energy for the two conduction were calculated. The AC electrical conductivity shows a normal behaviour according to the relation ac=A . The exponent  was calculated for different values of x and was found to be temperature and composition dependent. The spectral behaviour of both dielectric constant and the loss tangent tan  at different ferequency and temperature were investigated. Keywords Germanium Gallium selenide – Gallium selenide – Germanium selenide ( GeGaSe – GaSe – GeSe) thin films; Thermal evaporation techniques; X-Ray Diffraction (XRD); Scanning Electron Microscopy (SEM); Transmission Electron Microscopy (TEM); Differential scanning caliometry (DSC); Optical properties; Electrical Properties.