Point defect-driven switching of conductivity type in Bi₂Te₃ films prepared by atomic layer deposition

Bismuth telluride (Bi₂Te₃) films have significant application prospects in future thin-film thermoelectric devices. Atomic layer deposition (ALD) offers significant advantages for the fabrication of high-performance nanoscale films due to its precise thickness control. However, due to the difficulty in synthesizing (Et₃Si)₂Te, there are relatively few reports on the preparation of Bi₂Te₃ based on the ALD method. In this study, intrinsic Bi₂Te₃ films with thicknesses below 22 nm are successfully deposited on substrates with varying thicknesses of SiO₂ by adjusting the number of ALD cycles (50-600). The results indicate that the thickness of amorphous SiO₂ can affect the crystallinity of films, thereby influencing the number of point defects in Bi₂Te₃ and causing a conversion between conductive types N and P to occur during heating and cooling. Based on the results of thermoelectric performance tests, this study proposes a relevant transformation mechanism. The carrier concentration of the prepared Bi₂Te₃ films reaches about 10²⁰ cm^-3 at room temperature, and a maximum power factor of 24.727 μW cm^-1 K^-2 is achieved at 453 K. This study reveals the influence of nanoscale crystallinity differences on the thermoelectric properties of Bi₂Te₃ thin films.