Thickness effects on the microstructure and electrical/thermoelectric properties of co-evaporated Bi-Te thin films

In this study, we investigated the effect of film thickness on the electrical and thermoelectric properties of bismuth-tellurium (Bi-Te) films. Bi-Te films of 1-, 4-, 10-, and 18-μm thicknesses were deposited via co-evaporation. Microstructural analyses using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy indicated columnar film growth, with a highly porous structure that increased with the film thickness. The electron mobility of the films decreased significantly as the film thickness increased, which may be explained by the film porosity. Given a fairly constant Seebeck coefficient, the power factor decreased significantly with film thickness: 2.8 mW/mK2 for the 1-μm-thick film and 1.5 mW/mK2 for the 18-μm-thick Bi-Te film.