Challenges of Topological Insulator Research: Bi₂Te₃ Thin Films and Magnetic Heterostructures

Abstract

Topological insulators (TIs) are of particular interest in the recent solid‐state research because of their exceptional features stemming from the conducting, topologically protected surface states. The exotic properties include the occurrence of novel quantum phenomena and make them promising materials for spintronics and quantum computing applications. Theoretical studies have provided a vast amount of valuable predictions and proposals, whose experimental observation and implementation, to date, are often hindered by an insufficient sample quality. The effect of even a relatively low concentration of defects can make the access to purely topological surface states impossible. This points out the need of high‐quality bulk‐insulating materials with ultra‐clean surfaces/interfaces, which requires sophisticated sample/device preparations as well as special precautions during the measurements. Herein, the challenging work on 3D TI thin films with a focus on is reported. It covers the optimization of the molecular beam epitaxy growth process, the in situ characterization of surface states and transport properties, the influence of exposure to ambient gases and of capping layers, as well as the effect of interfacing TI thin film with magnetic materials.

Enhancement of the Surface Morphology of (Bi0.4Sb0.6)2Te3 Thin Films by In Situ Thermal Annealing

“…At this stage, the randomly oriented crystals are not yet fully eliminated. To ensure a better nucleation of the BST film in the initial growth process, the same annealing procedure was repeated for a 5 nm film deposited at a lower deposition temperature (200 °C versus 225 °C), to increase the sticking coefficient of the adatoms [ 24 , 37 , 38 ]. The final result, presented in Figure 5 c,d, is striking.…”

High-Sensitivity Flexible Photodetectors Based on Bi2Te3/Rubrene Schottky Heterojunction with Superior Interface

“…Note that it is bonded covalently inside each QL, while the bonding is weak van der Waals force between different QLs. 4 Therefore, due to its intriguing atomic configurations, the high-purity TI Bi 2 Te 3 film with a layer-by-layer crystal structure and the highest degree of order can be naturally obtained on arbitrary substrates during the thermal growth process. Significantly, the crystalline defects and lattice disorders can be effectively controlled, and such surface state with a Dirac cone-type dispersion can be easily maintained.…”

“…Each QL in the Bi 2 Te 3 crystal is stacked by five atomic layers within the vertical −[Te (2) –Bi–Te (1) –Bi–Te (2) ]– arrangement. Note that it is bonded covalently inside each QL, while the bonding is weak van der Waals force between different QLs . Therefore, due to its intriguing atomic configurations, the high-purity TI Bi 2 Te 3 film with a layer-by-layer crystal structure and the highest degree of order can be naturally obtained on arbitrary substrates during the thermal growth process.…”

Quantum transport and potential of topological states for thermoelectricity in Bi2Te3 thin films

“…The material Bi 2 Te 3 has a rhombohedral crystal structure consisting of quintuple layers (QLs) of bismuth and tellurium atoms bound to each other (stacking sequence: Te [1]-Bi-Te [2]-Bi-Te [1]) through weak Van der Waals (VdW) forces, see figures 1(a) and (b). Bi 2 Te 3 is a prime member of 3D TIs that is most extensively studied due not only to its fascinating TI properties [15,[19][20][21][22][23], but also its excellent room-temperature thermoelectric (TE) properties [24,25]. By exploiting these properties, Bi 2 Te 3 has been used to fabricate flexible TE devices with a wide range of technological applications, for example in self-powered wearable electronics, electrical power-generation devices and precision temperature control of microchips [26][27][28][29][30][31][32].…”