الفهرس | Only 14 pages are availabe for public view |
Abstract A systematic investigation of the structural, optical and electrical properties of Se52In48-xPbx compositions (where x = 28, 31, 36 and 40 at.%) were carried out. The bulk materials of Se52In48-xPbx were prepared by the fusion and cooling technique. Thin films of Se52In48-xPbx were deposited under vacuum (10-5 Torr) on glass substrates by thermal evaporation technique of the bulk compositions. Results of x-ray diffraction for the powder compositions and thin films were reported and discussed. There is only one x-ray standard card for In0.03Pb0.97Se number 01- 089 - 3921, which is available for us and was used for structural identification of the experimentally prepared powder and films. The analysis of the x-ray diffraction patterns for the prepared powder of Se52In48-xPbx (where x = 28, 31, 36 and 40 at.%) show that the dominant crystalline phase are hexagonal InSe and cubic In0.03Pb0.97Se structure. The x-ray diffraction patterns of as deposited and annealed films were found to be in polycrystalline state.The optical transmission and reflection spectrum of these films were measured in the range 1000 - 2200 nm and the optical constants (absorption coefficient α, refractive index n, extinction coefficient k, real r and imaginary part i of the dielectric constant) were calculated for Se52 In48-x Pbx compositions films as a function of photon energy. The absorption data revealed the existence of allowed direct and indirect transitions. It has been found that the optical band gap decreases with increasing Pb content up to x = 36 at.% then, increases as Pb content raised up to 40 at.%. The results were interpreted in terms of the change in the average bond energy of the films as a function of composition. The increase of the optical energy gap at x = 40 at.% could be attributed to the decrease in the grain size, the reduction in disorder and decrease in density of localized states in the band gap. On the other hand, the values of direct and indirect optical energy gap of Se52In48-xPbx films was found to be increased with increasing the annealing temperature (90, 165 and 300 °C for one hour) and it was analyzed on the basis of the theory proposed by Mott and Davais. But for high percentage of Pb (x = 40 at.%) the optical energy decreases with annealing temperature (300 °C) and this is due to the production of surface dangling bond around the crystallites during the process of crystallization.The temperature dependence of dc conductivity for the as deposited films of Se52 In48-xPbx in the temperature range (303 – 423 K) was measured. For these films, it is suggested that the conduction is due to thermally activated process through the extended states. The effect of composition on the pre-exponential factor o and the activation energy E were studied. It is found that the values of o and E decreases with increasing Pb content (x = 28, 31, and 36 at.%) but for higher concentration of Pb (x = 40 at.%) o and E were increased. Frequency and temperature dependencies of the ac conductivity ac of Se52 In48-xPbxwere studied. It is found that ac() increases linearly with increasing frequency and the absolute temperatures. The values of the ac activation energy E() decreases with increasing frequency. This decrease may be attributed to the increase of the applied field frequency which enhances the electronic jump between the localized states. In addition it has been found that the activation energy of the dc conductivity is higher than that of ac, because of the existence of the electric field related to energy frequency affected on the charge carriers mobility as well as decreasing the ac activation energy. The values of the activation energy E decreases with increasing the Pb content up to 36 at.%. But for x = 40 at.% the value of E increases. This is confirmed with the results of optical energy gap (Eg) and dc activation energy (E). The dielectric constant was found to decrease with increasing frequency. The decrease of for the films with increasing frequency can be attributed to the contribution of many components of polarization, ionic, dipolar or orientation and space charge. On the other hand the dielectric constant was found to increase as the temperature increases over the whole investigated range of frequency. This is attributed to the fact that dipoles in polar materials cannot orient themselves at low temperature. When the temperature is increased the orientation of dipoles is facilitated and thus increases the orientational polarization and in turn increases . The dielectric loss was calculated and it is observed that decreases with increasing frequency due to the migration of ions in the material at low frequencies, and ion vibrations at high frequencies. On the other hand increases with increasing temperature, which can be attributed to the fact that orientational polarization is associated with the thermal motion of molecules leading to the increase of |