A.H. Moharram

The effect of annealing on the optical absorption and electrical conduction of amorphous As24.5Te71Cd4.5 thin films

Abstract The optical absorption of as-prepared and thermally annealed As 24.5 Te 71 Cd 4.5 thin films was measured. The optical energy gap E o increased from 0.58 to 0.85 eV with increasing thickness of the as-prepared films from 58 to 125 nm. Films annealed at temperatures higher than 423 K showed a decrease in E o . The electrical conductivity of the as-prepared and annealed films was measured in the temperature range 80–300 K. An amorphous-crystalline transformation was observed after annealing at temperatures higher than 423 K. The results obtained are discussed on the basis of amorphous-crystalline transformations.

Experimental studies of the Ge-Sb-Se system

Abstract A systematic study was made of the semiconducting chalchogenide glass system Ge 20 Sb x Se 80− x with 5 x N ( E ), at the Fermi energy, on the annealing temperature.

Electrical properties and structural changes of thermally co-evaporated CuInSe films

Abstract Thermal co-evaporation technique (from two sources — Cu wire and In30Se70 ingots) was used to prepare CuInSe thin films. Controlling the evaporation rates from the sources was helpful to get films having different Cu/In content. The temperature dependence of the electrical conductivity was investigated in the temperature range 80 K ≤T≤435 K . The density of localized states at the Fermi level and the activation energy for conduction are decreased on increasing the film (Cu/In) content. The activation energy for conduction of the Cu20In20Se60 film decreases on increasing the annealing temperature. Tetragonal CuInSe2 and hexagonal Cu2Se crystalline phases resulting from heat treatment have been identified using X-ray diffractometry and transmission electron microscope.

Pre-crystallization kinetics of the Bi10Se90 glass

Differential scanning calorimetry (DSC) results of Bi10 Se90 glass under non-isothermal conditions are reported. In the present work, the analyses have been focused on the endothermic peaks of the DSC curves. The models, used for calculation of the crystallization kinetics from the exothermic peaks, have been applied to obtain the pre-crystallization kinetics from the endothermic peaks. The activation energy of glass transition (Eg ), the Avrami index (n ) and the frequency factor (K 0 ) of the investigated glass are 186±0.2 kJ mol-1 , 2.08 and 2.5 × 1028 s-1 , respectively. The values obtained can be related to the kinetics of amorphous-crystalline transformations.

Calorimetric study of the chalcogenide Se72.5Te20Sb7.5 glass

The crystallization kinetics of the chalcogenide Se72.5Te20Sb7.5 glass were obtained using differential scanning calorimetry (DSC). The results of DSC curves, performed at different heating rates (α), have been reported and discussed. The activation energy for the crystallization of the investigated glass was found to be equal to 84.2±3.5 kJ mol-1. A non-integer value of the Avrami index (n = 3.5) indicated that two crystallization mechanisms, two-dimensional and three-dimensional growth, are working simultaneously with an equal share through the amorphous-crystalline transformations.

Electrical conductivity and crystallization kinetics of Se70Te30 films

Glassy Se70Te30 thin films were thermally evaporated onto chemically cleaned glass substrates. Crystallization kinetics were determined under isothermal conditions. DC conductivity of the investigated film was used as a parameter to calculate the crystallized fraction χ(t). The values obtained for the activation energy of crystallization and the Avrami index were 239.8±0.5 kJ/mol and 2.21±0.1, respectively. The non-integer value of the Avrami index indicates that two crystallization mechanisms, one- and two-dimensional growth, are responsible for the crystallization process.

The effect of silver incorporation on the properties of co-evaporated arsenic telluride thin films

Abstract Electrical resistivity and optical absorption of amorphous As 2 Te 3 :Ag co-evaporated films are investigated as a function of the Ag content up to 25 at%. The film resistivity decreased from 2.1 × 10 4 to 2.6 × 10 2 ω cm and the activation energy for conduction decreased from 0.45 to 0.36 eV with increasing the film Ag content. The dependence of the optical absorption coefficient on the photon energy is ascribed by the relation ( αhv ) = B ( hv − E 0 ) 2 . The optical gap E 0 of the as-prepared films decreases with increasing Ag content. The tail width of the localized states at the band gap was calculated and it increases with increasing the Ag content. The effect of the thermal annealing on the optical absorption was investigated. The changes were attributed to the thermally induced transformations in the chalcogenide films.

Short and intermediate range order of Ge20Se80−xTex glasses

The total structure factor, S(K), have been obtained for the chalcogenide Ge20Se80−xTex (where x=0, 10, 20, and 30 at. %) glasses using x-ray diffraction in the wave vector interval 0.28≤K≤6.87 A−1. The appearance of the first sharp diffraction peak in the structure factor indicates the presence of the intermediate range order. The radii of the first- and second-coordination shells (r1,r2) are increased linearly with Te addition. The large covalent radius of Te atom in compare with that of Se atom was behind the above linear increase. The first coordination number shows insignificant changes with Te content. The obtained values of r1/r2 ratio and the corresponding bond angle (Θ) indicate that the structural units inside the present alloys are Ge(Se1/2)4 tetrahedra connected by chains of the chalcogen atoms. Raman spectra confirm the above conclusion and in the same time exclude the existence of Ge(Te1/2)4 tetrahedra. Based on the chemical ordered network mode, Te–Te bonds are responsible for the different...

Crystallization kinetics and activation energies in the Bi-Se-In glassy system

Abstract Crystallization kinetics of the Bi10Se90−xInx glasses with x = 5, 10, and 20 at % have been studied under non-isothermal conditions. From the heating rate dependence of Tg and Tp, values of the activation energy for the glass transition (Et) and the activation energy for crystallization (Ec) are evaluated and their composition dependence discussed. DSC thermograms and X-ray diffractograms are useful in clarifying the role of In content on the crystallization phases and the electrical resistivity of these glasses. The results indicate that the crystallization mechanism involves several complex processes and that bulk crystallization with three-dimensional growth dominates over the other crystallization processes.

Crystallization kinetics of thermally evaporated As45.2Te46.6In8.2 thin films

Abstract Glassy As45.2Te46.6In8.2 thin films were thermally evaporated onto chemically cleaned glass substrates. Crystallization kinetics were determined under isothermal conditions. Heating the film up to the isothermal temperature with different rates was found to yield films with different electrical characterization. Conductivity of the investigated film was used as a parameter indicating the crystallized fraction χ(t). The obtained values of the activation energy for crystallization, the frequency factor and the Avrami index are (100±0.5) kJ/mol, (7.31±0.04) 108 s−1 and 1.45, respectively. The non-integer value of the Avrami index indicates that two crystallization mechanisms are responsible for the crystal growth.