• I M Ashraf

      Articles written in Pramana – Journal of Physics

    • Characteristics of photoconductivity in thallium monosulfide single crystals

      I M Ashraf H A Elshaikh A M Badr

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      This work elucidates the photoconductivity (PC) of thallium monosulfide single crystals. Results are obtained in the 77-300 K temperature range, 1500-4500 V lx excitation intensity, 6-18 V applied voltage, and in the 640-1500 nm wavelength range. Both the ac-photoconductivity (ac-PC) and the spectral distribution of the photocurrent are studied in different values of light intensity, applied voltage and temperature. Dependencies of carrier lifetime on light intensity, applied voltage and temperature are also investigated as a result of the ac-PC measurements. The temperature dependence of the energy gap width was described by studying the dc-photoconductivity (dc-PC).

    • Crystal growth, electrical and photophysical properties of Tl2S layered single crystals

      A M Badr H A Elshaikh I M Ashraf

      More Details Abstract Fulltext PDF

      The Tl2S compound was prepared in a single crystal form using a special local technique, and the obtained crystals were analysed by X-ray diffraction. For the resultant crystals, the electrical properties (electrical conductivity and Hall effect) and steady-state photoconductivity were elucidated in this work. The electrical measurements extend from 170 to 430 K, where it was found that $\sigma_{\perp} = 8.82 \times 10^{−5}$ Sm-1 when current flow direction makes right angle to the cleavage plane of the crystals. In the same range of temperatures, it was found that $\sigma_{\parallel} = 4.73 \times 10^{−5}$ Sm-1 when the current flow is parallel to the cleavage plane. In line with the investigated range of temperatures, the widths of the band gaps were calculated and discussed as also the results of the electrical conductivity and Hall effect measurements. In addition, the anisotropy of the electrical conductivity $(\sigma_{\perp} / \sigma_{\parallel})$ for the obtained crystals was also studied in this work. Finally the photosensitivity was calculated for different levels of illumination as a result of the photoconductivity measurements, which showed that the recombination process in Tl2S single crystals is a monomolecular process.

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