Showing papers by "V. Damodara Das published in 1989"
TL;DR: In this article, the size dependence of thermoelectric power and electrical resistivity have been analyzed by the effective mean free path model of size effect, and it is found that both the thermoeellectric powers and the electrical resistivities are linear functions of the reciprocal of thickness of the films.
Abstract: Crystalline Sb2Te3 thin films of different thicknesses have been prepared by subsequent annealing (at 500 K) of vacuum deposited, as‐grown, amorphous thin films of Sb2Te3 prepared on glass substrates at room temperature. Thermoelectric power and electrical resistivity of these annealed (crystalline) films have been determined as a function of temperature. The size dependence of thermoelectric power and electrical resistivity have been analyzed by the effective mean free path model of size effect. It is found that both the thermoelectric power and the electrical resistivity are linear functions of the reciprocal of thickness of the films. The data from the analyses of thermoelectric power and electrical resistivity have been combined to evaluate important material parameters such as carrier concentration, their mean free path, Fermi energy, and effective mass. The values of some of these are compared with the previous available values from literature.
42 citations
TL;DR: In this paper, it was found that the electrical resistivity of the air-exposed films is much higher than that of the as-grown (unexposed) thin films.
Abstract: Thin films of PbTe of different thicknesses have been prepared on glass substrates at room temperature by vacuum deposition. It is found that the electrical resistivity of the air-exposed films is much higher (by about 2 to 3 orders of magnitude) than that of the as-grown (unexposed) thin films. The electrical resistivity temperature behaviours of both the air-exposed and as-grown (unexposed) thin films of PbTe are different but both show hysteresis behaviour during successive heating-cooling cycles. These observations can be explained by considering that the desorption of absorbed gas molecules (mainly oxygen) and creation of defects at higher temperatures during heating influence the electrical conduction. Further, the time factor involved in gas desorption-adsorption can cause the observed hysteresis in temperature-dependent conduction behaviour. The as-grown (unexposed) thin-film conductivity exhibits the expected reciprocal thickness dependence due to the thickness effect, but the air-exposed film conductivity does not. This can be explained to be due to the complete masking of the thickness effect by the gas adsorption effect in air-exposed film conductivity. The reciprocal thickness dependence observed in the case of unexposed film conductivity has been explained by the 'effective mean free path' model. The low value of the 'grain boundary' mean free path obtained by the analysis points to the fact that in polycrystalline films, grain boundary scattering is extensive and controls the film conductivity.
23 citations
TL;DR: In this article, the phase transition temperatures (located by a steep change in resistance and thermoelectric power with temperature) during heating and cooling are different, thereby showing a thermal hysteresis during phase transition.
Abstract: Electrical conductivity and thermoelectric power measurements as a function of temperature have been carried out on Ag2Te thin films of different thicknesses prepared on glass substrates at room temperature in a vacuum of 5×10−5 Torr. It is found that the phase transition temperatures (located by a steep change in resistance and thermoelectric power with temperature) during heating and cooling are different, thereby showing a thermal hysteresis during the phase transition. It is also found that the magnitude of the hysteresis is a function of thickness, increasing with decreasing thickness. This can be due to the large surface‐to‐volume ratio, small grain size, and a large density of dislocations in thin films.
17 citations
TL;DR: In this article, Pichard et al. measured the thermoelectric power of thin films of the alloy Se20Te80 of different thicknesses between 600 and 1250 A on clean glass substrates at room temperature in a vacuum of 5 × 10-5 Torr by the vacuum deposition technique.
2 citations