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Mixed; semiconductors; co-precipitation; optical characterization; thermoelectric power.

The polycrystalline Pb_𝑥Zn_1–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 Pb_𝑥Zn_1–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 Pb_𝑥Zn_1–𝑥S samples may be due to reduced grain boundary potential. In Pb_𝑥Zn_1–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.

M Nagabhushanam¹ E Nagabushan² D Jaya Prakash² B Rajam² K Yadaiah³

1. Department of Physics, University College of Science, Osmania University, Hyderabad 500 007, India
2. University College of Technology, Osmania University, Hyderabad 500 007, India
3. S.V. Degree and P.G. College, Suryapeta, Nalagonda (Dist) 508 213, India

Published

February 2009

Manuscript received

1 May 2008