Thermoelectric power and figure of merit of Pb-Sn-Te alloy thin films

This paper describes the results of thermoelectric measurements carried out by our group on Pb-Sn-Te alloy thin films of different compositions, prepared by vacuum thermal flash evaporation. The compositions studied were Pb_0.8Sn_0.2Te, Pb_0.6 Sn_0.4Te, Pb_0.5Sn_0.5Te and Pb_0.4Sn_0.6Te. Thin films of the ternary alloy Pb _0.8Sn_0.2Te with excess 1% Te doping was also studied to see the effect of excess Te on the thermoelectric properties. The electrical resistivity of the films was also measured simultaneously, and both the thermoelectric power and electrical resistivity data were analyzed by the effective mean free path model. Out of the compositions studied, it was found that 1% Te excess doped Pb _0.8Sn_0.2Te alloy thin films showed the best thermoelectric power and figure of merit values. However, these values were lower than the bulk values as is to be expected due to the high electrical resistivity of thin films compared to the bulk. Whereas the thermoelectric power of Pb_0.8Sn_0.2Te thin films was of the order of 240 μV/K, the thermoelectric power of thin films of other compositions was around 150-180 μV/K only. It was found that thicker films showed a higher figure of merit whereas thinner films showed a lower figure of merit. This is due to the fact that thinner film resistivity is higher than the thicker ones due to the classical size effect, i.e., larger additional surface scattering contribution. The details of the results obtained on different composition thin films are discussed