Identifying the Manipulation of Individual Atomic-Scale Defects for Boosting Thermoelectric Performances in Artificially Controlled Bi₂Te₃ Films.

Abstract

The manipulation of individual intrinsic point defects is crucial for boosting the thermoelectric performances of n-Bi₂Te₃-based thermoelectric films, but was not achieved in previous studies. In this work, we realize the independent manipulation of Te vacancies V_Te and antisite defects of Te_Bi and Bi_Te in molecular beam epitaxially grown n-Bi₂Te₃ films, which is directly monitored by a scanning tunneling microscope. By virtue of introducing dominant Te_Bi antisites, the n-Bi₂Te₃ film can achieve the state-of-the-art thermoelectric power factor of 5.05 mW m^-1 K^-2, significantly superior to films containing V_Te and Bi_Te as dominant defects. Angle-resolved photoemission spectroscopy and systematic transport studies have revealed two detrimental effects regarding V_Te and Bi_Te, which have not been discovered before: (1) The presence of Bi_Te antisites leads to a reduction of the carrier effective mass in the conduction band; and (2) the intrinsic transformation of V_Te to Bi_Te during the film growth results in a built-in electric field along the film thickness direction and thus is not beneficial for the carrier mobility. This research is instructive for further engineering defects and optimizing electronic transport properties of n-Bi₂Te₃ and other technologically important thermoelectric materials.