• M Nagabhushanam

      Articles written in Bulletin of Materials Science

    • Growth, characterization and transport properties of Pb𝑥Zn1–𝑥S mixed crystals

      M Nagabhushanam E Nagabushan D Jaya Prakash B Rajam K Yadaiah

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      The polycrystalline Pb𝑥Zn1–𝑥S semiconductor powder with (0 ≤ 𝑥 ≤ 0.5) has been prepared by controlled co-precipitation method from an alkaline medium using thiourea as a sulphide ion source. Pellets are made with these powders applying 10 ton/sq.cm. pressure and sintered at 800°C for 2 h in nitrogen atmosphere. X-ray studies of these samples have indicated that the compounds are polycrystalline in nature with mixed hexagonal and cubic structure of ZnS and cubic structure of PbS. Lattice parameters (𝑎 and 𝑐) of all the compounds are determined from the X-ray data and are found to decrease nonlinearly with increase in Pb concentration (𝑥). It is also observed that the grain size of the crystallites increases in samples with 𝑥 = 0–0.5. Scanning electron micrographs have shown that both cubic and hexagonal crystallites are present in the mixed crystals. The electrical conductivity in Pb𝑥Zn1–𝑥S is found to decrease with increase in composition (𝑥 = 0–0.5), whereas it increases at all temperatures in all samples. Mobility of charge carrier concentration is found to increase with increasing temperature. The increase in carrier mobility in Pb𝑥Zn1–𝑥S samples may be due to reduced grain boundary potential. In Pb𝑥Zn1–𝑥S samples with 𝑥 = 0–0.3, the sum of the activation energy due to charge carriers and grain boundary potential is equal to the activation energy due to conductivity.

    • Effect of copper doping on structural, optical and electrical properties of Cd0.8Zn0.2S films prepared by chemical bath deposition

      K Hadasa G Yellaiah M Nagabhushanam

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      Cd0.8Zn0.2S:Cu films of 1.3–6.1 mole percentage of copper have been grown on mica substrate by using chemical bath deposition technique. The films have been characterized by using XRD, SEM and UV spectrophotometer. X-ray diffraction studies have shown that the films are polycrystalline. The average crystallite size as measured from XRD data is in the range of 125–130 nm. The activation energies of Cd0.8Zn0.2S:Cu films, as observed from d.c. conductivity studies in the temperature range (77–300 K) studied, decreased with the increase in Cu concentration. The optical absorption studies have revealed that the energy gap increases gradually with an increase in Cu concentration, whereas conductivity studies have shown an anomalous increase in conductivity in films of 3.8 mole percentage of Cu. SEM pictures have revealed the presence of defects with spherical structure having fibre network. The variation of electrical conductivity is explained based on the defects present and by adopting tunneling mechanism.

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