Nanocrystalline PbTe thin films are prepared by thermal evaporation on glass substrates. The investigations of X-ray diffractograms have shown that the structure of film is found to possess stable face centred cubic (fcc) phase in which the grains predominantly grow in the direction of (200) plane. The grain size of the films is within the range of 27–43 nm. Morphologies like assembly of nanoparticles, worm-like structures and nanocubes were prepared by tuning the film thickness. Electrical resistivity is measured using four-probe technique and its thickness dependence has been analysed on the basis of ‘effective mean free path model’. A change in conductivity from 𝑛-type to 𝑝-type is observed due to the increase of migration of tellurium vacancies in the films with temperature. Bandgap energy of the PbTe nanocrystalline thin films suffered a large blue shift of about 1.299 eV due to quantum confinement of charge carriers. The nanocrystalline PbTe thin films of different morphologies such as nanoparticles, wormlike and nanocubes have the optical bandgap energies of 1.61, 1.23 and 1.01 eV, respectively. Photoconductivity measurement shows that the prepared nanocrystalline PbTe thin films of different morphology exhibits good response. This structure induced change in optical properties may have potential applications in optoelectronics devices.
Volume 43, 2020
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