A. E. Bekheet

The switching phenomenon in amorphous In2Te3 thin films

Abstract Investigation of the switching phenomenon in amorphous ln2Te3 films revealed that it is typical for a memory switch. The thickness dependence of the mean value of the switching voltage Vth was linear in the investigated range and V th decreased exponentially with a temperature rise from 298 to 373 K. The switching voltage activation energy (ϵ) calculated from the temperature dependence of V th is about 0.25 eV. The conduction activation energy (Eσ) obtained from the temperature dependence of film resistance was found to be 0.51 eV. The agreement between the obtained value of the ratio ϵ E σ (0.49) and those of the temperature difference between that inside the film and that of its surface with their values obtained before suggests that the switching phenomenon in the investigated In2Te3 films may be explained according to an electrothermal model for the switching process.

Effect of annealing on the electrical properties of ln2Se3 thin films

Abstract Thin film samples of In 2 Se 3 were prepared from synthesized polycrystalline ln 2 Se 3 by a thermal evaporation technique. X-ray analysis show that the synthesized material has α-phase structure, while the as-deposited films have an amorphous structure. The films have β-phase structure after annealing at temperature ⩾ 523 K. The conduction activation energy ( E σ ) of the as-deposited samples, as obtained from the temperature dependence of the electrical conductivity, is 0.391 eV. The obtained value of E σ was explained according to a previously postulated band structure of the investigated material. The electrical conductivity of the investigated samples behaves differently with time after annealing at different elevated temperatures. On one hand, E σ decreased for samples after annealing at 423 and 473 K to 0.313 and 0.262 eV respectively; this may be due to the increase of the degree of ordering in the investigated compound with annealing. On the other hand, E σ increased for samples after annealing at 523 K to 0.787 eV; this is due to its crystallization to the β-phase, as confirmed by its X-ray diffraction pattern.

Effect of annealing on the structural and electrical properties of In2Te3

Amorphous In2Te3 was prepared in both bulk form, by quenching the molten material, and thin-film form, by the thermal evaporation technique. X-ray diffraction analysis showed that the prepared samples in bulk and as-deposited thin-film forms were in the amorphous state. β- and α-phases of In2Te3 were prepared by annealing bulk samples at 615 and 813 K, respectively. Films annealed at 573 K give β-phase polycrystalline structure. The electrical conductivity for the as-deposited In2Te3 films increases with increasing film thickness. The conduction activation energy, ΔEσ, of the as-prepared bulk and thin film samples were found to be 0.516 and 0.521 eV. The corresponding values of room-temperature electrical conductivity, σRT, for these samples are 1.1×10-6 and 7.15×10-7Ω-1m-1, respectively. The observed change in the value of σRT may be due to the difference in the structure of bulk and thin-film samples. The increase of ΔEσ with annealing temperature for both bulk and thin-film samples is interpreted in terms of the density of states model proposed by Mott and Davis.

The effect of Cd addition on the optical properties of Se70Te30 films

Se70Te30 and Se70Te20Cd10 films of different thicknesses were prepared by a thermal evaporation technique. Transmittance and reflectance data are measured for the films obtained, in the wavelength range 400–2500 nm. The optical constants, the refractive index n and the absorption index k, are calculated by an accurate method using Murmanns exact equations. It is found that values of n at any wavelength for Se70Te30 films are larger than that for Se70Te20Cd10 films. From the analysis of the optical constants it was found that the optical energy gap (Egopt) and the width of the tails of the localized states in the gap region (Ee) increase while the high frequency dielectric constant decreases with the addition of Cd.

Conduction mechanism in amorphous In2III X3VI thin films

Amorphous In2IIIX3VIfilms (X = Te or Se) are obtained by vacuum thermal evaporation of bulk materials on glass substrates. The current - voltage characteristics in the temperature range 298–378 K and in the thickness range 212–652 nm exhibited a transition from an ohmic region in the lower field followed by non-ohmic region in the high field region, which has been explained by the anomalous Poole-Frenkel effect. The temperature dependence of current in the ohmic region is of thermally activated process. The variation of dielectric constant with temperature is investigated for the two compounds.