Thickness dependence of the electrical and thermoelectric properties of co-evaporated Sb2Te3 films

P-type antimony telluride (Sb2Te3) films of various thicknesses (1-, 6-, 10-, and 16-mu m) were deposited on an oxidized Si (100) substrate at 250 degrees C by effusion cell co-evaporation. Microstructural analysis using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy revealed that the grains of the films grew in a mode in which recrystallization was prevalent and grain growth subdued, in contrast to typical film growth, which is often characterized by grain growth. The resultant microstructure exhibited narrow columnar grains, the preferred orientation of which changed with film growth thickness from (1010) with the 1-mu m films to (015) for the 6- and 10-mu m films, and finally(110) for the 16-mu m films. Carrier mobility and the overall thermoelectric properties of the Sb2Te3 films were affected significantly by changes in the film microstructure; this was attributed to the strong anisotropy of Sb2Te3 regarding electrical conductivity. The highest power factor of 3.3 mW/mK(2) was observed for the 1-mu m-thick Sb2Te3 film. (C) 2017 Elsevier B.V. All rights reserved.