Transport properties of Bi/sub 2/Te/sub 2.4/Se/sub 0.6/ thin films

Abstract

High efficiency thermoelectric thin film converters find applications as miniature energy sources which can deliver low power at high output voltage and also as IR detectors and sensors in new developments like microelectronics, space applications, medicine, etc. Bi/sub 2/Te/sub 3-x/Se/sub x/ chalcogenide is an important thermoelectric material which needs to be investigated for its thermoelectric properties in the thin film state. In this paper we present our results on thermoelectric properties of Bi/sub 2/Te/sub 2.4/Se/sub 0.6/ thin films. Annealed thin films of Bi/sub 2/Te/sub 2.4/Se/sub 0.6/ material, grown on glass plates held at room temperature by the flash evaporation technique in a vacuum of 2/spl times/10/sup -5/ torr, were investigated for their thermoelectric and electrical properties in the temperature range 300 K-480 K. The non-stoichiometry problem as encountered in the thermal evaporation method is avoided in this simple flash evaporation technique as evidenced from the EDAX compositional analysis. Structural analysis indicated the polycrystalline nature of the films with hexagonal structure. Grain size was calculated from electron micrographs. Thermoelectric studies indicated n-type conductivity. As temperature increases, thermoelectric power of the films increases in the low temperature range and then decreases after reaching a maximum. This is explained to be due to the evaporation of volatile components. The important physical parameters like Fermi energy, power index of the energy dependent mean free path expression and carrier concentration were evaluated from these measurements using the size effect theory.