Synthesis of Bi2Te3 Single Crystals with Lateral Size up to Tens of Micrometers by Vapor Transport and Its Potential for Thermoelectric Applications

Bismuth telluride (Bi2Te3) has recently attracted significant attention owing to its unique physical properties as a three-dimensional topological insulator and excellent properties as a thermoelectric material. Meanwhile, it is important to develop a synthesis process yielding high-quality single crystals over a large area to study the inherent physical properties and device applications of two-dimensional materials. However, the maturity of Bi2Te3 vapor-phase synthesis is not good, compared to those of other semiconductor two-dimensional crystals. In this study, therefore, we report the synthesis of relatively large-area Bi2Te3 crystals by vapor transport method, and we investigated the key process parameters for a synthesis of relatively thin and large-area Bi2Te3 crystals. The most important factor determining the crystal synthesis was the temperature of the substrate. A Bi2Te3 device exhibited a considerable photocurrent when the laser was irradiated inside the electrode area. This indicated that the photo-thermoelectric effect was the main mechanism of generation of photocurrent. The estimated Seebeck coefficient of the device was similar to 1.96 mu V/K, which is comparable to the previously reported high Seebeck coefficient of Bi2Te3. This synthesis method can guide the development and applications of various types of layered crystals with the space group of R (3) over barm.