• B K Sarma

      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.

    • Synthesis of nanocrystalline CdS thin films in PVA matrix

      R Devi P Purkayastha P K Kalita B K Sarma

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      Nanocrystalline thin films of CdS are deposited on glass substrates by chemical bath deposition technique using polyvinyl alcohol (PVA) matrix solution. Crystallite sizes of the nanocrystalline films are determined from broadening of X-ray diffraction lines and are found to vary from 5.4–10.2 nm. The band gap of the nanocrystalline material is determined from the UV spectrograph. The absorption edge is shifted towards the lower wave length side (i.e. blue shift) and are found to be within the range from 2.48–2.8 eV as grain sizes decrease from 10.2–5.4 nm. This is also supported by the spectral response curves. An increase of molarity decreases the grain size which in turn increases the band gap.

    • Structural characterization of lead sulfide thin films by means of X-ray line profile analysis

      N Choudhury B K Sarma

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      X-ray diffraction patterns of chemically deposited lead sulphide thin films have been recorded and X-ray line profile analysis studies have been carried out. The lattice parameter, crystallite size, average internal stress and microstrain in the film are calculated and correlated with molarities of the solutions. Both size and strain are found to contribute towards the broadening of X-ray diffraction line. The values of the crystallite size are found to be within the range from 22–33 nm and the values of strain to be within the range from 1.0 × 10-3–2.5 × 10-3.

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