• S L Sharma

      Articles written in Bulletin of Materials Science

    • Photoelectronic properties of HgI2 crystals for nuclear radiation detection

      S L Sharma H N Acharya

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      Photoelectronic properties of red mercuric iodide single crystals, grown from its saturated solution in tetrahydrofuran, have been studied for the wavelength range 450-700 nm at temperatures 80, 110, 175, 235 and 300 K. Various aspects of the optical generation of charge carriers have been discussed. The computer simulation of the room temperature photoconductivity has generated the optimized values of the mobility-lifetime products (𝜇e𝜏e = 5.67 × 10-5 cm2/V, 𝜇h𝜏h = 0.18 × 10-5 cm2/V), and surface recombination velocities (𝑆e = 3.2 × 105 cm/s, 𝑆h = 4.5 × 105 cm/s) of the charge carriers in these crystals. The estimated values of the electron and hole drift lengths for typical electric fields suggest that, under the negative electrode illumination, THF 𝛼-HgI2 crystals have high potential as regards to their use as phptodetectors in most of the scintillation spectrometers.

    • Effect of gamma radiation on optical and electrical properties of tellurium dioxide thin films

      T K Maity S L Sharma

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      Gamma radiation induced changes in the optical and electrical properties of tellurium dioxide (TeO2) thin films, prepared by thermal evaporation, have been studied in detail. The optical characterization of the as-deposited thin films and that of the thin films exposed to various levels of gamma radiation dose clearly show that the optical bandgap decreases with increase in the gamma radiation dose up to a certain dose. At gamma radiation doses above this value, however, the optical bandgap has been found to increase. On the other hand, the current vs voltage plots for the as-deposited thin films and those for the thin films exposed to various levels of gamma radiation dose show that the current increases with the gamma radiation dose up to a certain dose and that the value of this particular dose depends upon the thickness of the film. The current has, however, been found to decrease with further increase in gamma radiation dose. The observed changes in both the optical and electrical properties indicate that TeO2 thin films can be used as the real time gamma radiation dosimeter up to a certain dose, a quantity that depends upon the thickness of the film.

    • Effect of gamma radiation on electrical and optical properties of (TeO2)0.9 (In2O3)0.1 thin films

      S L Sharma T K Maity

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      We have studied in detail the gamma radiation induced changes in the electrical properties of the (TeO2)0.9 (In2O3)0.1 thin films of different thicknesses, prepared by thermal evaporation in vacuum. The current–voltage characteristics for the as-deposited and exposed thin films were analysed to obtain current versus dose plots at different applied voltages. These plots clearly show that the current increases quite linearly with the radiation dose over a wide range and that the range of doses is higher for the thicker films. Beyond certain dose (a quantity dependent on the film thickness), however, the current has been observed to decrease. In order to understand the dose dependence of the current, we analysed the optical absorption spectra for the as-deposited and exposed thin films to obtain the dose dependences of the optical bandgap and energy width of band tails of the localized states. The increase of the current with the gamma radiation dose may be attributed partly to the healing effect and partly to the lowering of the optical bandgap. Attempts are on to understand the decrease in the current at higher doses. Employing dose dependence of the current, some real-time gamma radiation dosimeters have been prepared, which have been found to possess sensitivity in the range 5–55 𝜇Gy/𝜇A/cm2. These values are far superior to any presently available real-time gamma radiation dosimeter.

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