Temperature and size effects on electrical properties and thermoelectric power of Bismuth Telluride thin films deposited by co-sputtering

N-type Bismuth telluride thin films of different thicknesses were deposited on cleaned glass substrate at room temperature by co-sputtering technique. The films were annealed at 300 °C for 12 h in nitrogen atmosphere to improve their properties. The thermoelectric power and electrical properties measurements were carried out on the films with thickness from 70 nm to 480 nm in the temperature range 300–430 K. The thickness dependence of electrical resistivity and Seebeck coefficient of annealed films was analyzed using the effective mean free path model. Some physical parameters such as effective mean free path of charge carriers in hypothetical bulk, the exponent of the energy term of mean free path, activation energy, and the Fermi energy were calculated. Both the electrical conductivity and the Seebeck coefficient of the bismuth telluride films increased with increasing of film thickness and grain size. Films with fewer grain boundaries and defects have longer effective mean free path of carriers and the mean free path decreases with the increase of temperature. The electron–phonon interaction was considered as the main scattering mechanism in the annealed bismuth telluride thin films.