Synthesis and thermal instability of high-quality Bi2Te3/Sb2Te3 superlattice thin film thermoelectrics

The quality and temperature stability of 1 nm Bi2Te3/5 nm Sb2Te3 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 degrees C. The interdiffusion preferably starts next to superlattice defects. At 300 degrees C the Bi2Te3 and Sb2Te3 layers were mostly interdiffused, forming the thermodynamically stable Sb1.66Bi0.33Te3 alloy. The data suggests that structural integrity of Bi2Te3/Sb2Te3 superlattices will not be stable for extended times above 200 degrees C, thus inhibiting application of such superlattice s over a wide temperature range.