M.M. Hafiz

Effect of composition on the structure and electrical properties of As‐Se‐Cu glasses

As‐Se‐Cu glasses, with Cu content varying between 5 and 25 at. %, were produced by quenching from the melt. The values of resistivity and activation energy for conduction decreased continuously with increasing the copper content. Memory switching phenomena was observed in glasses containing Cu less than 20 at. %. Glasses containing higher Cu concentration showed a reverse switching cycle. Thermally induced changes in the structural properties have been examined using x‐ray diffraction, differential thermal analysis, and scanning electron microscopy. The results were discussed on the basis of thermally induced transformations.

Kinetics study of non-isothermal crystallization in Se0.7Ge0.2Sb0.1 chalcogenide glass☆

Abstract Differential scanning calorimetry data at different heating rates on Se 0.7 Te 0.3 chalcogenide glass are reported and discussed. From the heating rate dependence of values of T g , T c and T p , the glass transition activation energy, E t , and the crystallization activation energy, E c , were derived. The crystallization data are interpreted in terms of recent analyses developed for non-isothermic crystallization and also for the evaluation of E c and the characterization of a crystallization mechanism. The results indicate that bulk crystallization with two-dimensional growth occurs for this glass. The calculated E t and E c are 143 ± 3 and 174 ± 8 kJ/mol, respectively.

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.

Reversible phase change in BixSe100−x chalcogenide thin films for using as optical recording medium

Abstract The microstructure of electron beam deposited Bi x Se 100− x thin films (where x varies from 0 to 16 at.%) was investigated. The morphology of crystallization for in situ thermally annealed and electron beam heated Bi 16 Se 84 films was investigated using transmission electron microscopy. Selected area electron diffraction was used to characterize different phases observed during the crystallization process where the crystalline Bi 2 Se 3 phase was separated. Optical absorption measurements were carried out on as-deposited Bi x Se 100− x films of different compositions. It was found that the mechanism of the optical absorption follows the rule of non-direct transition. The optical energy gap decreases with increasing Bi content. The effect of thermal annealing on the optical properties of Bi 16 Se 84 films was investigated. The study indicated that Bi 16 Se 84 films have low threshold energy for amorphization, high optical absorption coefficient and optimum contrast between the amorphous and the crystalline states. The decrease in the optical gap is discussed on the basis of amorphous-crystalline transformations.

DTA studies on the crystallization of InxSe1 − x chalcogenide glasses

Abstract Results of differential thermal analysis (DTA) under nonisothermal conditions on five chalcogenide glasses of the In x Se 1 − x system ( x = 0.05, 0.10, 0.15, 0.20 and 0.25 at.) are reported and discussed. The crystallization mechanism has been studied by using DTA, scanning electron microscopy (SEM) and X-ray diffraction. From the dependence of the glass transition temperature ( T g ), the onset crystallization temperature ( T c ) and the crystallization peak temperature ( T p ) on the heating rate (α), the glass transition activation energy ( E t ) and the crystallization activation energy ( E c ) were derived. The calculated E t for In x Se 1 − x varied between 246 and 309 kJ/mol. The results indicate that bulk crystallization with two-dimensional growth occurs for these glasses. The average activation energy of crystallization for In x Se 1 − x varied between 105 and 125 kJ/mol. In 0.10 Se 0.90 chalcogenide glass showed a minimum value of E c as well as ( T c - T g ), which represents the thermal stability of the glass, indicating that this composition has a tendency towards crystallization more than the other compositions.

Short- and medium-range order in Se-Ge glassy systems. I: Effect of composition

Abstract From the X-ray diffraction data of Se1-xGex chalcogenide glasses (0 0.1, the results indicate that the amorphous phase has medium-range order or topology order.

On the structure of As2Te3 glass

X-ray scattering has been used to investigate the structure of glassy As2Te3, prepared by quenching in liquid nitrogen. The result of the coherent scattered x-ray intensity proved that the medium-range order (MRO) is very weak, and this was attributed to the higher metallic nature of the glass. Analysis of the first two peaks in the curve of the total radial distribution function, T(r), revealed that the short-range order (SRO) in the glassy state is different from that in the crystalline state, and that the first coordination sphere includes As–As and Te–Te bonds in addition to the As–Te bonds.

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.

Optical investigations on InxSe1−x thin films (II)

Abstract Thin films of In0.10Se90 of thickness ∾200 A are prepared by vacuum evaporation. The optical gaps (Eoptg) and the high-frequency dielectric constant (eϵ∞) are determined from the absorption spectrum of the In0.10Se0.90 films heat-treated at different temperatures. The effect of the temperature of heat treatment on the optical gap (Eoptg) and the high-frequency dielectric constant (eϵ∞) of the films is interpreted in terms of the density of state model of Mott and Davis and explained as being due to the saturation of bonds in the amorphous solid. It is shown that in the case of In0.10Se0.90 a transition from the amorphous to the crystalline state takes place at ∾373 K. The structural analysis of In0.10Se0.90 films by using XRD is reported.