Enhanced electrical properties of stoichiometric Bi0.5Sb1.5Te3 film with high-crystallinity via layer-by-layer in-situ Growth

The preparation of high-performance Bi2Te3-based films is vitally important for the miniaturization of Bi2Te3 thermoelectric (TE) device. Herein, a series of stoichiometric Bi0.5Sb1.5Te3 films with different preferential orientations have been fabricated through in-situ crystallization during the co-sputtering process. We discover that the preferential orientation was transformed from (011̅5) to (101̅10) to (000l) orientation with increasing the substrate temperature. The (000l)-oriented films exhibit the best electrical transport properties, which the maximum electrical conductivity of 8.0×104 S·m-1 and power factor of 3.8 mW K-2·m-1 are much more than those of the bulk material. The excellent properties are attributed to the high-crystallinity, well-controlled preferential orientation, and minimized compositional deviation. A layer-by-layer in-situ growth model is proposed to understand the formation mechanism of the (000l)-oriented films. Our work demonstrates that the electrical transport performance of Bi2Te3-based films can be remarkably improved through finely controlling the crystallinity and preferential orientation under the condition of stoichiometric composition.