• H L Das

      Articles written in Bulletin of Materials Science

    • Structural characterization of vacuum evaporated ZnSe thin films

      Pradip Kr Kalita B K Sarma H L Das

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      Thermally evaporated ZnSe thin films deposited on glass substrates within substrate temperatures (Ts)at 303 K-623 K are of polycrystalline nature having f.c.c. zincblende structure. The most preferential orientation is along [111] direction for all deposited films together with other abundant planes [220] and [311]. The lattice parameter, grain size, average internal stress, microstrain, dislocation density and degree of preferred orientation in the film are calculated and correlated withTs.

    • Space charge limited conduction in CdSe thin films

      Pradip Kr Kalita B K Sarma H L Das

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      The current (𝐼)–voltage (𝑉) characteristics of thermally evaporated CdSe thin films having thickness in the range 850–3000 Å and deposited within the substrate temperature of 303–573 K show nearly linear dependence at low voltage and afterwards a non-linear behaviour at higher voltage range. A detailed study of 𝐼–𝑉 curves in dark and under illumination clearly reveals the mechanism as ohmic at low voltage and that of trap limited space charge limited conduction (SCLC) at higher voltage. The transition voltage (𝑉𝑡) from ohmic to SCLC is found to be quite independent of ambient temperature as well as intensity of illumination. SCLC is explained on the basis of the exponential trap distribution in CdSe films. Trap depths estimated from the ln 𝐼 vs 103/T plots are found to be within 0.60–0.37 eV. Using the relevant SCLC theory, the carrier concentration, 𝑛0, total trap concentration, 𝑁t, and the ratio of free charge to trapped charge, 𝜃 , have been calculated and correlated with ambient temperature and intensity of illumination.

    • Photoconductivity of ZnTe thin films at elevated temperatures

      N Mazumdar R Sarma B K Sarma H L Das

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      Photoconductivity of thermally evaporated ZnTe thin films was studied at different elevated temperatures. A gap type cell configuration with Al electrodes on glass substrates was used. The conductivity was found to obey two distinct conduction mechanisms within the region of applied fields. At low fields the photoconduction is ohmic and at high fields it is of Poole–Frenkel type. With increase of ambient temperatures, the Poole–Frenkel conductivity regions were found to extend to lower fields. The temperature dependence of dark conductivity also was found to be of similar nature.

    • Some spectral response characteristics of ZnTe thin films

      R Sarma N Mazumdar H L Das

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      Zinc telluride thin films have been grown at room temperature and higher temperature substrates by thermal evaporation technique in a vacuum of 10-6 torr. A main peak in the photocurrent is observed at 781 nm (1.58 eV) with two lower amplitude peaks on the lower wavelength side and one on higher wavelength side. The evaluated thermal activation energy is found to correspond well with the main spectral peak. From these studies it can be inferred that temperatures up to 453 K is still in the extrinsic conductivity region of the studied ZnTe thin films.

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