E. Abd El-Wahabb

Optical properties of Sb2Se3 thin films

Abstract The optical constants (the refractive index n and the absorption index k) of Sb2Se3 thin films deposited at room temperature on quartz have been calculated in the wavelength range (5000–2000 nm) using a transmission spectrum. Both n and k were found to be practically independent on either time, up to 6 months, or the film thickness in the range of 102–760 nm. Beyond the absorption edge, the absorption is due to allowed indirect and direct transitions with energy gaps of 1.225 and 1.91 eV, respectively. The value of the optical gap depends on the annealing temperature. X-ray analysis showed that the prepared films at room temperature had amorphous structure while the films annealed at 200°C for 1 h were verified to be crystalline.

Switching phenomenon in amorphous Sb2Se3

Abstract The switching phenomenon in amorphous Sb 2 Se 3 films was found to be a memory switch. The OFF-state was found to have three forms for the voltage and current relation. The threshold voltage (switching voltage) showed thickness and temperature dependence and increased with increasing thickness and/or decreasing temperature. The ratio of the activation energy at switching and the thermal conduction activation energy was 0.5, and the calculated values of the temperature inside the active region at the moment of switching make explanation of the memory type switching in Sb 2 Se 3 films possible on the basis of the electrothermal breakdown process.

Theoretical and experimental study of the conduction mechanism in Sb2 Se3 alloy

To understand the nature of Sb2 Se3 semiconductor as a bulk sample, the X-ray diffraction study was carried out to identify the sample structure. Dc and ac electrical properties measured in the temperature range 290–370 K, and frequency range 102–105 Hz were the subject of the present work. Properties such as dielectric constant ζ\, loss function tanδ, and electrical conductivities σac as a function of both frequency and temperature are reported. Different models of electrical conduction in semiconductor materials have been used to explain the observed results. A trail has been made to correlate the results of this paper with the average heat of atomization HS and the average coordination number M. The experimental and theoretical investigation is in accordance with Liang criterion.

Electrical resistivity of crystalline Sb2Se3

Abstract Resistivity variations of bulk and crystallized Sb 2 Se 3 films of different thicknesses were studied at different temperatures. The dark electrical resistivity decreases with increasing film thickness. For substrate temperatures below the crystallization temperature, resistivity variations were characteristic of amorphous films and for greater temperatures an anomalous initial resistivity increase was observed. At higher working temperatures the transition region was not observed. Positive decreasing TCR values were obtained up to 340 K after which a negative constant value was attained for polycrystalline films. While the resistivity and the conduction activation energy decreased with increasing film thickness, the free charge carrier concentration increased and gave a value of the order 10 12 −10 16 cm −3 for the bulk material.

Structural variations in antimony selenide

Abstract DTA graphs, X-ray diffraction patterns and electron micrographs showed that bulk Sb2Se3 obtained by furnace cooling or quenching the melt from 1123 K to room temperature has a crystalline nature of orthorhombic structure while the prepared thin films with any thickness showed amorphous structure. The sharp endothermic peak at 603 K showing phase transition extended as a plateau to about 623 K with the quenched material depending on the degree of crystallinity. Crystallization of thin films was attained by annealing at 423 K in air and at 448 K under vacuum. This amorphous into crystalline transformation showed itself as an additional exothermic peak at 453 K in the DTA graph. Increasing the temperature and time of annealing and also the film thickness enhanced crystallization which was found to start with the preferred orientation on the planes (020), (120) and (130). The observed structural changes were explained in view of the variations of atomic energy and internal stresses, the nature of boundary angles, the chain and layer structure of Sb2Se3 and the role played by surface defects during crystallization.

Thickness and temperature dependence of the electrical resistivity of amorphous Sb2Se3 films

Abstract Films of Sb2Se3 with different thicknesses deposited at a rate of 30 A s − at room temperature were found to have amorphous structure. The dark electrical resistivity of Sb2Se3 films with silver electrodes increased with increasing thickness reaching a maximum value at 370.8 nm after which it decreased with increasing thickness. For all thicknesses resistivity decreased with increasing temperature. Up to 335 K, conduction was activated by 0.15 eV characterizing an extrinsic conduction region. In the range 300–500 K, 0.9 eV activated conduction for samples with thickness greater than 400 nm and 1.17 eV activated conduction in thicknesses less than 400 nm. Above 560 K a sudden drop in resistivity took place which was attributed to Mott transition. Charge carrier concentration in the bulk material assumed the value 2.9 × 1011 cm−3 on the basis of an empirical formula for the charge carrier concentration dependence on thickness. Decreasing negative TCR values were obtained with increasing temperature. The results were explained in view of the injecting and the blocking nature of the electrodes, change of stoichiometry of the film, heterogeneous and island film structure, variations in the number of trapping centres and conduction by either tunnelling or hopping mechanisms.

Electrical and optical properties of (Sb2Se3)2 (Sb2Te3)1 thin films

A study of the synthesized (Sb2Se3)2 (Sb2Te3)1 glassy system has been carried out, X-ray diffraction (XRD) patterns and differential thermal analysis (DTA) of the system studied were used to obtain an insight into the structural information. An investigation of the electrical and optical properties of (Sb2Se3)2 (Sb2Te3)1 thin films prepared by thermal evaporation having different thicknesses (89.2, 214, 223 nm) and annealing temperatures ranging from 300 to 473 K has been carried out. The effect of the thickness and heat treatment on the activation energy ΔE for d.c. conductivity and the density of localized states at the Fermi level N(EF) were carried out. The electrical conductivity measurements depend on the thickness and annealing temperature, and exhibit two types of conduction mechanisms. Optical absorption measurements have been made on as-deposited and annealed films for the investigated system. The optical transition was found to be indirect. The optical energy gap (Eopt) decreases with increasing thickness and annealing temperatures (below Tg). The corresponding band is approximately twice the conduction activation energy. This effect is interpreted in terms of the density of states model proposed by Mott and Davis.