Thermoelectric power of Se<inf>20</inf>Te<inf>80</inf> alloy thin films: Temperature and size effects

Thin films of the alloy Se20Te80 of different thicknesses between 600 and 1250 Å were deposited on clean glass substrates at room temperature in a vacuum of 5 × 10-5 Torr by the vacuum deposition technique in individual evaporations. The thermoelectric power of these films was determined by measuring the developed thermo-e.m.f. at different temperature differences between the ends using the integral method. It was found that the thermoelectric power decreased with reciprocal temperature linearly. From the slope of the plot, the height of the Fermi level, which is pinned, was evaluated to be about 100 meV. It was also found that the room temperature thermoelectric power of the various films is an inverse function of thickness of the films. A similar inverse thickness dependence was also observed at 350 and 400 K. However, the thickness dependence is very small and is thought to be due to the specularity parameter's being close to unity. The reciprocal thickness dependence of the thermoelectric power of the films is explained on the basis of the size effect theory of Tellier (C.R. Tellier, Thin Solid Films, 51 (1978) 311) and Pichard et al. (C.R. Pichard, C.R Tellier and A.J. Tosserm J. Phys. F, 10 (1980) 2009) termed the "effective mean free path theory" which takes into account the effects of both the surface and the grain boundary scattering in thin films. © 1989.