Seebeck Effect and Giant Linear Magnetoresistance Affected by Conflicting n‐ and p‐Type Defect‐Induced Doping in Epitaxial Bi₂Te₃ Layers

Abstract

further raising the magnetoresistance magnitude, it is urgent to clarify the mechanism of the GLM effect, which remains unsettled so far.In the present work, we investigate the thermoelectric properties at room temperature (RT) and the (electrical) magnetotransport properties at T = 0.3 K in Bi 2 Te 3 layers that were epitaxially grown on the InP substrates by hot wall epitaxy. The hot wall epitaxy method that we employed for growing the Bi 2 Te 3 layers has the advantages of low cost, simplicity, and relatively large growth rates. As is typical for the chalcogenides, the Bi 2 Te 3 layers were unintentionally doped as intrinsic defects-generated free carriers. For Bi 2 Te 3 layers, the synthesis temperature plays particularly an important role for their physical properties as Te tends to re-evaporate due to its large vapor pressure when the temperature rises. We demonstrate by analyzing the Hall and Seebeck coeffi cients that the densities of defect-induced donors and acceptors exhibit unexpected dependencies on the growth temperature as if they compete with each other for the existence. It is then revealed that the GLM effect occurs in the layers when the Fermi level approaches the location of the Dirac point. We nevertheless attribute the GLM effect to the bulk states.In Figure 1 a, we show the dependence of the Seebeck coefficient S on the temperature T g of the layer growth in the hot wall epitaxy. The measurements were carried out at RT. The samples were prepared in four separate growth runs (#1, #2, #5, and #6), as distinguished by the symbol type in Figure 1 a,b. (The two sets #1 and #2 were previously investigated with respect to the structural properties in ref.[18]) The thickness d of the Bi 2 Te 3 layers was in the range of 0.15-1.3 µm (see Figure 1 b). One fi nds that S changed with T g in a complicated manner. In the growth of Bi 2 Te 3 layers, our previous study has established that the rapid re-evaporation of Te resulted in a deviation of the composition in the layers from stoichiometry for high growth temperatures. [ 18 ] For T g > 350 °C, the Bi content increased signifi cantly with increasing T g . We show the anticipated Bi content x in the layers by the dotted curve in Figure 1 b. The change in the densities of the defect-induced donors and acceptors is primarily responsible for the variation of S with T g

Bulk vs. Surface Structure of 3d Metal Impurities in Topological Insulator Bi2Te3

“…Additionally, the introduction of magnetic impurities into Bi-chalcogenides can break time-reversal symmetry and open an energy gap at the Dirac point of the surface states 9–11 . Recently, Bi 2 Te 3 and related systems with dilute doping of 3 d -metal atoms (Ti, V, Cr, Mn, and Fe) have been found to have ferromagnetic transitions at low temperatures.…”

“…The Bi-chalcogenides such as Bi 2 Te 3 and Bi 2 Se 3 have long been known for their thermoelectric properties 1 , 2 , but recently they have gained a great deal of attention as three-dimensional topological insulators with a large band gap and a single Dirac cone on the surface 3 – 8 . Additionally, the introduction of magnetic impurities into Bi-chalcogenides can break time-reversal symmetry and open an energy gap at the Dirac point of the surface states 9 – 11 . Recently, Bi 2 Te 3 and related systems with dilute doping of 3 d -metal atoms (Ti, V, Cr, Mn, and Fe) have been found to have ferromagnetic transitions at low temperatures.…”

Axiotaxy of Bismuth Telluride Films on InP(111)B by High-Temperature Hot Wall Epitaxy

“…We emphasize that changing T g has significant consequences for Bi 2 Te 3 films in the transport properties and the Seebeck coefficient, as previously investigated in similarly grown films in refs and . The electrical conduction was of p -type in optimally grown films, whereas n -type conduction took place when the growth temperature was moved away from the optimal window . Free carriers are supplied in Bi 2 Te 3 from crystalline defects, and so the dominant defect is indicated to change with T g .…”

Bulk Rashba Spin Splitting and Dirac Surface State in p‐Type (Bi0.9Sb0.1)2Se3 Single Crystal

“…The value of S decreases with decreasing T down to 2 K, displaying a shoulder at as indicated by an arrow. [ 40 ] The H dependence of S is recorded at selected T , shown in Figure S4, Supporting Information, where H is applied along the [001] direction. The value of , defined as [, is plotted with T at H = 70 kOe, in the inset of Figure 2a.…”