A. A. El-Shazly

Optical properties of ternary ZnS x Se1−x polycrystalline thin films

Ternary ZnSxSe1−x polycrystalline thin films were prepared by evaporation in vacuum of 10−5 Torr. The molecular fractionx varied in the region o≦x≦1. The optical constants (the refractive indexn, the absorption indexk, and the absorption coefficientα) were determined in the wavelength range 300–1600nm. A plot representingα2=f(hv) shows that the ZnSxSe1−x polycrystalline thin films of different compositions have two direct transitions corresponding to the energy gapsE andE+Δ. The variation in eitherE orE+Δ withx indicates that this system belongs to the amalgamation type. Such variation follows a quadratic equation. The bowing parameter was found to be 0.456 eV, roughly equal to the calculated value 0.60 eV using the empirical pseudopotential method based on the virtual-crystal approximation, in which the disorder effect has not been taken into account.

Anomalous photovoltaic effect in thin films of ZnSe obliquely deposited in vacuum

An anomalous photovoltaic effect (APE) has been observed in thin films of zinc selenide obliquely deposited in vacuum for the first time. Photovoltages of up to 70 V have been measured in some samples. The effect is influenced strongly by some experimental parameters. The changes in the photovoltages may be attributed to the film structure which has been investigated during the course of this study.

Structural, electrical and optical properties of Cdx Zn1−xSe thin films

X-ray diffraction and electron diffraction techniques indicate that Cdx Zn1−xSe thin films on glass substrates have a polycrystalline nature, with sphalerite structure for x≤0.5 and wurtzite structure for x≥0.6. The crystalline size in each composition increases with increasing the film thickness. The room temperature dark resistivity π varies from one composition to another showing a transition at x=0.55The temperature dependence of π of the deposited films revealed two conduction mechanisms, one below 352 K due to shallow levels, surface states, and defects introduced during the film growth, and over 352 K due to deep-level ionization following the ordinary semiconducting behaviour.The thermal activation energy of the free charge carriers decreases linearly with increasing the molar fraction x of the CdSe content up to x=0.55, above which it increases with increasing x.The optical constants of Cdx Zn1−xSe thin films of different compositions were determined in the spectral range 400–2000 nm. The analysis of the absorption coefticient at and near the absorption edge indicates the existence of allowed direct transition energy gaps decreasing with increasing x.

The compositional dependence of the optical gap of Se75SbxGe25−x

The aim of this paper is threefold to determine the optical constants (n, k and α) of the glass system Se 75 Ge 25−x Sb x (x=1, 5, 15 and 20) in thin-film form in the wavelength range 400 to 1200 nm; to study the type of optical transitions that may occur; and to determine the corresponding band gap