A comprehensive review on Bi ₂ Te ₃ ‐based thin films: Thermoelectrics and beyond

Bi 2 Te 3 ‐based materials are not only the most important and widely used room temperature thermoelectric (TE) materials but are also canonical examples of topological insulators in which the topological surface states are protected by the time‐reversal symmetry. High‐performance thin films based on Bi 2 Te 3 have attracted worldwide attention during the past two decades due primarily to their outstanding TE performance as highly efficient TE coolers and as miniature and flexible TE power generators for a variety of electronic devices. Moreover, intriguing topological phenomena, such as the quantum anomalous Hall effect and topological superconductivity discovered in Bi 2 Te 3 ‐based thin films and heterostructures, have shaped research directions in the field of condensed matter physics. In Bi 2 Te 3 ‐based films and heterostructures, delicate control of the carrier transport, film composition, and microstructure are prerequisites for successful device operations as well as for experimental verification of exotic topological phenomena. This review summarizes the recent progress made in atomic defect engineering, carrier tuning, and band engineering down to a nanoscale regime and how it relates to the growth and fabrication of high‐quality Bi 2 Te 3 ‐based films. The review also briefly discusses the physical insight into the exciting field of topological phenomena that were so dramatically realized in Bi 2 Te 3 ‐ and Bi 2 Se 3 ‐based structures. It is expected that Bi 2 Te 3 ‐based thin films and heterostructures will play an ever more prominent role as flexible TE devices collecting and converting low‐level (body) heat into electricity for numerous electronic applications. It is also likely that such films will continue to be a remarkable platform for the realization of novel topological phenomena.