Synthesis and Thermal Instability of High-Quality Bi₂Te₃/Sb₂Te₃ Superlattice Thin Film Thermoelectrics

The quality and temperature stability of 1 nm Bi 2 Te 3 /5 nm Sb 2 Te 3 superlattices prepared by molecular beam epitaxy for the first time was investigated by in situ and ex situ X-ray diffraction and transmission electron microscopy. Upon heating, the superlattice structures are not stable against interdiffusion of the components, with micro- and nanostructural changes occurring at temperatures as low as 200 °C. The interdiffusion preferably starts next to superlattice defects. At 300 °C the Bi 2 Te 3 and Sb 2 Te 3 layers were mostly interdiffused, forming the thermodynamically stable Sb 1.66 Bi 0.33 Te 3 alloy. The data suggests that structural integrity of Bi 2 Te 3 /Sb 2 Te 3 superlattices will not be stable for extended times above 200 °C, thus inhibiting application of such superlattices over a wide temperature range.