Differential scanning calorimetry results under non-isothermal conditions of chalcogenide (Sb₁₅As₃₀Se₅₅)_100−xTe_x (where 0 ≤ x ≤ 10 at.%) glasses are reported and discussed. The dependence of the characteristic temperatures “glass transition temperature (T_g), the crystallization onset temperature (T_c) and the crystallization temperature (T_p)” on the heating rate (β) utilized in the determination of the activation energy for the glass transition (E_g), the activation energy for crystallization (E_c), the glass thermal stability (ΔT = T_c − T_g) and the Avrami exponent (n). The composition dependence of the T_g, E_g, and E_c were discussed in terms of the chemical bond approach, the average heats of atomization and the cohesive energy (CE). The diffractogram of the transformed material shows the presence of some crystallites of AsSb, Sb₄Te₆, As₂Se₃ and Sb₂Se₃ in the residual amorphous matrix.

The effect of heat treatment on the optical and electrical properties of Ge₁₅Sb₁₀Se₇₅ and Ge₂₅Sb₁₀Se₆₅ thin films in the range of annealing temperature 373–723 K has been investigated. Analysis of the optical absorption data indicates that Tauc's relation for the allowed non-direct transition successfully describes the optical processes in these films. The optical band gap (E_g^opt.) as well as the activation energy for the electrical conduction (ΔE) increase with the increase of annealing temperature (T_a) up to the glass transition temperature (T_g). Then a remarkable decrease in both the E_g^opt. and ΔE values occurred with a further increase of the annealing temperature (T_a>T_g). The obtained results were explained in terms of the Mott and Davis model for amorphous materials and amorphous to crystalline structure transformations. Furthermore, the deduced value of E_g^opt. for the Ge₂₅Sb₁₀Se₆₅ thin film is higher …

Amorphous Ge{sub 30}Sb{sub 10}Se{sub 60} chalcogenide thin films were prepared onto cleaned glass substrates using thermal evaporation technique. The structure of the as-prepared films was confirmed to be amorphous using X-ray diffraction. The optical absorption coefficient ({alpha}) for the as-deposited films was calculated by using reflectance and transmittance measurements in the wavelength range 400-900 nm. The optical constants (refractive index (n) and the extinction coefficient (k)) were controlled by Murman's exact equations. The effects of annealing temperature in the temperature range 300-658 K on the optical and electrical properties of the as-prepared Ge{sub 30}Sb{sub 10}Se{sub 60} thin films were discussed in details. It was found that both the optical band gap E{sub g}{sup opt} and the activation energy for electrical conduction {delta}E{sub dc} increase with increasing the annealing temperature up to the glass transition temperature (T{sub g}), followed by a remarkable decrease with the increase of annealing temperature above T{sub g}. The obtained results were interpreted on the basis of amorphous-crystalline transformations.

This paper reports photoelectrical properties of (As₃₀Sb₁₅Se₅₅)_100−xTe_x amorphous chalcogenide films (0 ⩽ x ⩽ 12.5 at.%) through measurements of ‘steady state’ and ‘transient’ photocurrents. The composition dependence of the steady state photocurrent at room temperature shows that the photoconductivity increases while the photosensitivity decreases with increasing Te content. A study of photoconductivity of (As₃₀Sb₁₅Se₅₅)_100−xTe_x at different levels of light intensity reveals that, the photoconductivity increases exponentially with increase in light intensity. The Photocurrent (I_ph) when plotted against light intensity (G) follows a power law (I_ph = G^γ) the exponent γ for (As₃₀Sb₁₅Se₅₅)_100−xTe_x films has been found nearly 0.5 suggesting bimolecular recombination. The transient photoconductivity shows that the lifetime of the carrier decreases with increasing the light intensity. This decrease suggests that …

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 T _g, the photobleaching is dominant for Ge₂₀Se_80−x Bi _x (x=0, 2.5, and 5 at.%), while for Ge₂₀Se_72.5Bi_7.5 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 E _o and E _d 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 effects of composition and thermal annealing near crystallization temperature, T {sub c} on the optical and structural properties of Ge{sub 20}Se{sub 80-} {sub x} Bi {sub x} (x=0, 2.5, 5 and 7.5 at%) was investigated. The influence of incorporation Bi content in Ge{sub 20}Se{sub 80-} {sub x} Bi {sub x} 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 E {sub g} 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 E {sub o} and E {sub d} 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, T_c on the optical and structural properties of Ge₂₀Se_80−xBi_x (x=0, 2.5, 5 and 7.5 at%) was investigated. The influence of incorporation Bi content in Ge₂₀Se_80−xBi_x 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 E_g 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 E_o and E_d were determined. The effect of annealing on the nature and degree of crystallization has been investigated by …

The temperature dependence of the DC electrical conductivity σ_DC was measured in the temperature range from 300–500 K. It was found that there are double activation energies, E_σ, for Ge₂₀Se_80−xBi_x (x=0, 2.5 and 5 at%) films, while there is single activation energy for Ge₂₀Se_72.5Bi_7.5. 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 E_σ 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 …

Amorphous (As₃₀Sb₁₅Se₅₅)_100−xTe_x (with 0 ≤ x ≤ 12.5 at.%) were prepared by thermal evaporation. The optical transmission and reflection spectra of these films were measured in the wavelength range of 400–900 nm. The mechanism of the optical absorption follows the rule of allowed non-direct transition. It was found that, the optical band gab E₀ decreases while the width of localized states (Urbach energy) E_c increases by increasing Te content. The relationship between E₀ and chemical composition of the (As₃₀Sb₁₅Se₅₅)_100−xTe_x system were discussed in terms of Cohesive energy (CE), the average heat of atomization H_s, and the average coordination number N_r. The later are computed from the heat of atomization and the coordination number of used elements, respectively.

Amorphous Sb₁₀Se₉₀ thin films were prepared by thermal evaporation of the bulk glass. The changes in the optical properties (transmittance, optical gap, absorption coefficient, refractive index and extinction coefficient) have been measured in the wavelength range 500–900 nm of virgin and ultraviolet (UV) illuminated films. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It is found that the optical energy gap decreases (photo-darkening) and the refractive index increases with the increase of UV exposure time. The dispersion of the refractive index (n) has been discussed in terms of Wemple–Didomenico single oscillator model. The oscillator energy E₀ and the dispersion energy E_d have been determined and discussed in terms of UV exposure time. The photo-darkening was discussed in terms of some of the current literature models.