Showing papers by "V. Damodara Das published in 1995"

Thermoelectric power of ternary semiconductor Se10Sb10Te80 thin films

Abstract: Thin films of different thicknesses in the range 400–1600 A have been vacuum deposited on clean glass substrates held at room temperature by very fast evaporation of the Se10Sb10Te80 bulk alloy. The thermoelectric power of these films has been measured as a function of temperature during heating and cooling cycles by the integral method. It is found that the thermoelectric power of these films is slightly different during the heating and the cooling cycles which is ascribed to slight reorientation of microcrystallites as also evidenced by x‐ray diffraction. It is further found that the thermoelectric power (at a constant temperature) is a function of film thickness; it varies nearly linearly with reciprocal thickness. From these data, the nature of carrier scattering in the films has been ascertained. From the energy‐dispersive x‐ray analysis patterns of the films the semiquantitative content of the constituent elements Sb, Se, and Te has been determined.

Thermoelectric Power Studies on 1% Excess Te Doped Pb$_{\bf 0.8}$Sn$_{\bf 0.2}$Te Thin Films

Abstract: Thin films of Pb0.8Sn0.2Te of thicknesses varying between 360 A and 3400 A have been prepared by flash evaporation on cleaned glass substrates held at room temperature. Thermoelectric power (TEP) of these films has been evaluated by measuring the thermal emf developed by the integral method in the temperature range 300 K to 500 K. It has been found that TEP of all the films is positive and increases with temperature in the low temperature region and tends to saturate at high temperatures, beyond 400 K. This has been attributed to the pinning of the Fermi level at high temperatures. It was also found that these films did not show the expected linear dependence of TEP on the inverse film thickness.

Electrical conduction in ternary semiconductor Ga5Se20Te75 thin films

Abstract: Different thickness thin films of the ternary alloy Ga5Se20Te75 have been vacuum deposited on clean glass substrates held at room temperature at a very fast rate. The film resistance has been measured as a function of temperature during two cycles of heating and cooling. It has been found that the resistance‐temperature (R‐T) variation of the films during first heating and cooling is different, the R‐T curve during heating lying above the R‐T curve during cooling in the case of thinner films and below in the case of thicker films. There are two possible explanations for the difference in resistance variation during heating and cooling and between the thinner and thicker films. The first is due to the semiconducting nature of the material and the second is due to the removal of frozen‐in defects and/or change in concentration depth profile. In addition to these, the phenomenon of self‐annealing can also take place in thicker films. Log resistance vs reciprocal temperature plots are found to be linear, indi...

Variation of electrical transport properties and thermoelectric figure of merit with thickness in 1% excess Te-doped Pb0.2Sn0.8Te thin films

Abstract: Pb0.2Sn0.8Te thin films of different thicknesses have been deposited on glass substrates by flash evaporation. Electrical resistivity and thermoelectric power measurements have been carried out in the temperature range 300-500 K as a function of film thickness. The thickness dependence of the electrical resistivity and thermoelectric power observed has been explained using the effective mean free path model of classical size effect theory. The thermoelectric power factor was calculated from the measured values of electrical resistivity and thermoelectric power. The thermoelectric power factor is found to be dependent on thickness and temperature. By taking thermal conductivity values from the literature, the thermoelectric figure of merit was also calculated and it was found that this too was dependent on the temperature and thickness.