The optical properties of as-deposited GexSe92-xIn8 (x = 10, 12.5, 15 and 20 at%) have been studied. Various optical constants have been calculated for the studied compositions. The mechanism of the optical absorption follows the rule of non-direct transition. It was found that, the optical energy gap (Eg) decreased with increasing Ge content. This result can be interpreted on the basis of the chemical-bond approach proposed by Bicermo and Ovshinsky. The values of the refractive index (n) and the extinction coefficient (k) increased with increasing Ge content. Annealing of Ge12.5Se79.5In8 films at temperature higher than the glass transition temperature was found to decrease the optical energy gap. Electrical conductivity was measured in the temperature range (300-450 K) for the studied compositions. The effect of composition on the activation energy (ΔE) and the density of localized states at the Fermi level N(EF) were studied. The electrical conductivity measurements show two types of conduction channels that contribute two conduction mechanisms. On the other hand, the electrical resistivity and the activation energy were found to decrease with increasing the annealing temperature. Transmission electron microscope (TEM) investigation indicates the separation of crystalline phase after annealing at the temperatures higher than the glass transition. The results were discussed on the basis of amorphous crystalline transformations

Amorphous Ag10Te90 thin films were prepared onto glass substrates using the thermal evaporation method. The effect of γ-irradiation on the optical parameters was investigated in the dose range 10–180 krad. The optical absorption coefficient (α) for the as-deposited and irradiated films has been determined from the reflectance (R) and transmittance (T) measurements in the wavelength range 400–900 nm. Analysis of the spectral behavior of the absorption coefficient in the absorption region revealed direct transitions. The optical studies showed the decrease in band gap (Eopt) with an increase in γ-irradiation . The width of the tails of localized states (Ee) were calculated and found to be increasing after γ-irradiation. Dielectric related optical constants, such as (n, kex., ε1 and ε2), were presented. Finally, the effect of γ-irradiation on the high-frequency dielectric constant (εL) and carrier concentration (N/m*) is also studied. The results were discussed by the change on the degree of disorder as well as the radiation-induced effect on solids.

Amorphous Ag10Te90 thin films were prepared onto glass substrates using the thermal evaporation method. The effect of γ-irradiation on the optical parameters was investigated in the dose range 10–180 krad. The optical absorption coefficient (α) for the as-deposited and irradiated films has been determined from the reflectance (R) and transmittance (T) measurements in the wavelength range 400–900 nm. Analysis of the spectral behavior of the absorption coefficient in the absorption region revealed direct transitions. The optical studies showed the decrease in band gap (Eopt) with an increase in γ-irradiation . The width of the tails of localized states (Ee) were calculated and found to be increasing after γ-irradiation. Dielectric related optical constants, such as (n, kex., ε1 and ε2), were presented. Finally, the effect of γ-irradiation on the high-frequency dielectric constant (εL) and carrier concentration (N/m*) is also studied. The results were discussed by the change on the degree of disorder as well as the radiation-induced effect on solids.

The temperature dependence of the DC electrical conductivity σDC was measured in the temperature range from 300-500 K. It was found that there are double activation energies, Eσ, for Ge20Se80-xBix (x = 0, 2.5 and 5 at%) films, while there is single activation energy for Ge20Se72.5Bi7.5. when incorporation of Bi = 7.5 at%, the pre-exponential value σ0 decreases by about six order of magnitude, the activation energy in the extended states Eσ decreases from 0.96 to 0.09 eV. Also the effect of applied electric field was studied and observed that, activation energy in high temperature region increases with increasing electric field; this behavior can be understood assuming that the contribution to the conductivity activation process is due to conduction in the extended states and also due to hopping in the localized states. With the increasing electric field, as former process, which is having high activation energy, becomes more predominant due to the dumping of the carriers in the extended states, the effective activation energy of the system increases, in spite of the fact that the activation energy of the extended states conduction may remain constant. Finally, the electrical data suggests that the addition of bismuth produces localized states near the conduction band edge so that the electrical transport is due to hopping of electrons after being excited into localized states at the conduction band edge.

The temperature dependence of the DC electrical conductivity σDC was measured in the temperature range from 300-500 K. It was found that there are double activation energies, Eσ, for Ge20Se80-xBix (x = 0, 2.5 and 5 at%) films, while there is single activation energy for Ge20Se72.5Bi7.5. when incorporation of Bi = 7.5 at%, the pre-exponential value σ0 decreases by about six order of magnitude, the activation energy in the extended states Eσ decreases from 0.96 to 0.09 eV. Also the effect of applied electric field was studied and observed that, activation energy in high temperature region increases with increasing electric field; this behavior can be understood assuming that the contribution to the conductivity activation process is due to conduction in the extended states and also due to hopping in the localized states. With the increasing electric field, as former process, which is having high activation energy, becomes more predominant due to the dumping of the carriers in the extended states, the effective activation energy of the system increases, in spite of the fact that the activation energy of the extended states conduction may remain constant. Finally, the electrical data suggests that the addition of bismuth produces localized states near the conduction band edge so that the electrical transport is due to hopping of electrons after being excited into localized states at the conduction band edge.

The effects of composition and thermal annealing near crystallization temperature, Tc on the optical and structural properties of Ge20Se80−xBix (x=0, 2.5, 5 and 7.5 at%) was investigated. The influence of incorporation Bi content in Ge20Se80−xBix system results in a gradual decrease in the indirect optical gap from 1.89 to 1.44 eV, this behavior can be explained as increased tailing. On annealing, the optical band gap Eg decreases gradually for the crystallized films while the refractive index increases, this behavior can be attributed to transformation from amorphous to crystalline and was explained in the light of dangling bond model. The refractive index n of as-prepared and annealed films has been analyzed according to the Wwmple–DiDominico single oscillator model and the values of Eo and Ed were determined. The effect of annealing on the nature and degree of crystallization has been investigated by studying the structure using transmission electron microscope, X-ray diffraction and scanning electron microscope.

The effects of composition and thermal annealing near crystallization temperature, Tc on the optical and structural properties of Ge20Se80−xBix (x=0, 2.5, 5 and 7.5 at%) was investigated. The influence of incorporation Bi content in Ge20Se80−xBix system results in a gradual decrease in the indirect optical gap from 1.89 to 1.44 eV, this behavior can be explained as increased tailing. On annealing, the optical band gap Eg decreases gradually for the crystallized films while the refractive index increases, this behavior can be attributed to transformation from amorphous to crystalline and was explained in the light of dangling bond model. The refractive index n of as-prepared and annealed films has been analyzed according to the Wwmple–DiDominico single oscillator model and the values of Eo and Ed were determined. The effect of annealing on the nature and degree of crystallization has been investigated by studying the structure using transmission electron microscope, X-ray diffraction and scanning electron microscope.

In addition to the conversion from p-type to n-type conductivity that occurs in Ge-Se-Bi thin films when Bi is incorporated in a certain concentration. We found that, when these films were illuminated to UV light, after being annealed at glass transition temperature Tg, the photobleaching is dominant for Ge20Se80-xBix (x=0, 2.5, and 5 at.%), while for Ge20Se72.5Bi7.5 photodarkening is dominant. The photoinduced changes in the optical constants were studied. The refractive index (n) has been analysed according to the Wwmple-DiDominico single oscillator model and the values of Eo and Ed for exposed and unexposed films were determined, respectively. The photostructural effects were discussed in the light of single-double well model proposed by Tanaka and chemical bond approach

The crystallization kinetics of Cu10Se90 and Cu20Se80 glasses at different heating rates have been studied by differential scanning calorimetry (DSC). The crystallization phases resulting from the DSC have been identified using X-ray diffraction (XRD). The DSC thermograms have been analyzed in terms of the activation energy, stability and dimensionality of growth by different models. Results of DSC are reported and discussed from the heating rates’ dependence of values of the glass transition temperature (Tg) and the peak temperature of crystallization (Tp). The characteristic temperatures of the studied chalcogenide glasses has been used to evaluate the glass-forming ability (GFA) by using various thermal stability parameters such as Hruby's criterion (HR). The activation energy for glass (Eg) and the crystallization activation energy (Ec) are derived. The crystallization results are interpreted in terms of recent analyses developed for non-isothermal crystallization and also for the evaluation of (Ec). The average value of the Avrami exponent comes out to be 3, indicating that, the crystallization process takes place via three-dimensional growth with bulk crystallization

The crystallization kinetics of Cu10Se90 and Cu20Se80 glasses at different heating rates have been studied by differential scanning calorimetry (DSC). The crystallization phases resulting from the DSC have been identified using X-ray diffraction (XRD). The DSC thermograms have been analyzed in terms of the activation energy, stability and dimensionality of growth by different models. Results of DSC are reported and discussed from the heating rates’ dependence of values of the glass transition temperature (Tg) and the peak temperature of crystallization (Tp). The characteristic temperatures of the studied chalcogenide glasses has been used to evaluate the glass-forming ability (GFA) by using various thermal stability parameters such as Hruby's criterion (HR). The activation energy for glass (Eg) and the crystallization activation energy (Ec) are derived. The crystallization results are interpreted in terms of recent analyses developed for non-isothermal crystallization and also for the evaluation of (Ec). The average value of the Avrami exponent comes out to be 3, indicating that, the crystallization process takes place via three-dimensional growth with bulk crystallization