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 ∼196 μV/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 R3̄m.