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 VTe and antisite defects of TeBi and BiTe in molecular beam epitaxially grown n-Bi2Te3 films, which is directly monitored by a scanning tunneling microscope. By virtue of introducing dominant TeBi 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 VTe and BiTe as dominant defects. Angle-resolved photoemission spectroscopy and systematic transport studies have revealed two detrimental effects regarding VTe and BiTe, which have not been discovered before: (1) The presence of BiTe antisites leads to a reduction of the carrier effective mass in the conduction band; and (2) the intrinsic transformation of VTe to BiTe 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.

A comprehensive review on Bi2Te3‐based thin films: Thermoelectrics and beyond

“…First, under a suitable T sub and a low growth rate, Bi 2 Te 3 ‐based thin films can be grown stably by the process of layer‐by‐layer growth and their microstructure is typified by the (00 l ) orientation. As documented by the MBE‐grown films in our laboratory and elsewhere, [ 88,100,101,105 ] the films grown under stable conditions are evidenced by the strictly c ‐oriented growth of QLs (determined by high‐resolution transmission electron microscope measurements) and by the sequentially stacked QLs on the surface (observed via atomic force microscope), see the bottom panel in Figure 2. Second, the (0 1 5) preferential orientation is usually present in Bi 2 Te 3 ‐based thin films that were grown under unstable conditions, for example, under a rather low T sub and at too high growth rates, see the middle panel in Figure 2.…”

“…As a result, as shown in Figure 4C, the band bending and the built-in electric field introduce extra scattering for the mobile charge carriers, and this leads to an obviously degraded carrier mobility in n-type Bi 2 Te 3 films. Further studies by Zhang et al [101,105] have confirmed the above conjecture by finely tuning the intrinsic defects. N-type Bi 2 Te 3 films with n-type antisites Te Bi as the dominant atomic defects, instead of V Te and Bi Te defects, showed improved carrier mobility of above 80 cm 2 V -1 s -1 , notably higher than the common values of μ ≤ 50 cm 2 V -1 s -1 .…”

“…Moreover, a firm command of the film growth and the quality of the resulting films is a prerequisite to achieveing an excellent TE performance and carrying out a successful exploration of intriguing physical phenomena realized in Bi 2 Te 3 -based films. [88,91,97,98,100,101] This has its origin in the weak vdW interactions between the adjacent QLs. In contrast, Bi 2 Te 3 -based thin films with crystalline orientations other than (00l) or even amorphous structures can be fabricated under unstable growth conditions.…”

Thermoelectric Performance Enhancement of Film by Pulse Electric Field and Multi‐Nanocomposite Strategy

“…[34][35][36][37] Therefore, there has been much work carried out on Bi 2 Te 3 films. [38][39][40][41][42][43][44][45] In regards to utilizing the enhancement methods of CNT compositing and porosity, which we have particularly focused on in this work, the thermal conductivity of Bi 0.4 Te 3 Sb 1.6 films decreases to 0.25 W m −1 K −1 by compositing porosity, resulting in the increase of ZT. [46] The TE properties of Bi 2 Te 3 films can also be enhanced by compositing carbon allotropes.…”

Bottom-Up (Cu, Ag, Au)/Al2O3/Bi2Te3 Assembled Thermoelectric Heterostructures

“…Compared with its bulk counterparts, nanostructured Bi 2 Te 3 film provides promising possibilities for enhanced TE properties and potential applications in micro/nanoelectromechanical systems (MEMS/NEMS) TE device [8]. The thermoelectric performance of Bi 2 Te 3 can be optimized by adjusting the (00l) orientation [9,10], pores [9,11], nanosheet boundary [12,13], and the intrinsic defects [14,15]. In addition, constructing a heterogeneous interface is also one of the effective methods to optimize the thermoelectric performance.…”