Fabrication and characterization of Bi_(0.4)Te_(3.0)Sb_(1.6) thin films by flash evaporation method

摘要

Bi_(0.4)Te_(3.0)Sb_(1.6) thin films on glass substrates are fabricated by a flash evaporation method. In order to enhance the transport properties of the thin films, annealing in argon ambient at atmospheric pressure is carried out for 1 h in the temperature range from 200 to 400 deg C. The structure of the thin films, in terms of homogeneous composition and crystallinity, is investigated by energy dispersive X-ray spectroscopy and X-ray diffraction, respectively. The microstructure of the thin films is examined using scanning electron microscopy. We confirm that as-deposited Bi_(0.4)Te_(3.0)Sb_(1.6) thin films have a mostly homogeneous structure except for a few extra stuck particles. At higher annealing temperatures, the crystallinity of the thin films is improved and the size of crystal grains increases to the same size as the film thickness. However, excessive high annealing temperatures cause porous thin films due to the evaporation of tellurium. The transport properties of the thin films, in terms of the electrical resistivity, the Seebeck coefficient and the thermoelectric power factor are determined at room temperature. By optimizing the annealing conditions, it is possible to obtain a high-performance thin film with a thermoelectric power factor of 12.2 mu W cm~(-1) K~(-2). We consider that the performance of the thin films is enhanced for optimized annealing because of reductions in the importance of grain boundary scattering.