Electrical and structural properties of Bi2Te3 and Sb2Te3 thin films grown by the nanoalloying method with different deposition patterns and compositions

摘要

Thin films of Bi2Te3 and Sb2Te3 were synthesized by the nanoalloying approach, which has recently been proven to yield V-VI compounds with good thermoelectric properties and has several advantages over "conventional" growth on hot substrates. Firstly, repeating layers of the elements Bi, Sb and Te with a thickness in the range between 0.2 nm and 2.4 nm were deposited on BaF2 (111) substrates in an MBE system at room temperature with different deposition patterns for different samples, i.e. in bilayer and quintuple stacks, with different starting layer thicknesses and different Te contents. Subsequently, the element layer stacks were annealed in order to induce crystallization and compound formation of Bi2Te3 and Sb2Te3 thin films. The annealed thin films were characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The transport properties, i.e. electrical conductivities, carrier concentrations, carrier mobilities, Seebeck coefficients and thermal conductivities, were determined at room temperature for several sets of starting layer thicknesses and deposition patterns depending on the Te content. The texture was found to be strongly influenced by the starting thicknesses of the elemental layers in the deposition pattern. Results of temperature dependent measurements of the Seebeck coefficient and electrical conductivity on one sample of nanoalloyed Bi2Te3 and Sb2Te3 together with results from temperature dependent in situ XRD investigations are presented.