Fermi-level tuning of the Dirac surface state in (Bi_1−xSb_x)₂Se₃thin films

Abstract

We report on the electronic states and the transport properties of three-dimensional topological insulator (Bi<sub>1-<i>x</i></sub>Sb<sub><i>x</i></sub>)<sub>2</sub>Se<sub>3</sub> ternary alloy thin films grown on an isostructural Bi<sub>2</sub>Se<sub>3</sub> buffer layer on InP substrates. By angle-resolved photoemission spectroscopy, we clearly detected Dirac surface states with a large bulk band gap of 0.2 - 0.3 eV in the (Bi<sub>1-<i>x</i></sub>Sb<sub><i>x</i></sub>)<sub>2</sub>Se<sub>3</sub> film with <i>x</i> = 0.70. In addition, we observed by Hall effect measurements that the dominant charge carrier converts from electron (n-type) to hole (p-type) at around <i>x</i> = 0.7, indicating that the Fermi level can be controlled across the Dirac point. Indeed, the carrier transport was shown to be governed by Dirac surface state in 0.63 ≤ <i>x</i> ≤ 0.75.These features suggest that Fermi-level tunable (Bi<sub>1-<i>x</i></sub>Sb<sub><i>x</i></sub>)<sub>2</sub>Se<sub>3</sub>-based heterostructures provide a platform for extracting exotic topological phenomena.

Designer Topological Insulator with Enhanced Gap and Suppressed Bulk Conduction in Bi2Se3/Sb2Te3 Ultrashort-Period Superlattices

“…More than an order of magnitude reduction in carrier density was obtained between the samples with larger periods (~12 nm) and those with smaller periods (~5 nm). The low carrier densities of our smaller period TI/TI SLs are comparable to the best values reported for the constituent TI materials grown by MBE directly on sapphire substrates 11,12,31,32 . We believe that these values can be significantly improved, as these results were achieved only by our first efforts.…”

2D Layered Material Alloys: Synthesis and Application in Electronic and Optoelectronic Devices

“…[156] Copyright 2017, American Chemical Society. [172] b,c) Reproduced with permission. [172] Copyright 2018, IOP Publishing Ltd. which are set to be opposite to the sources, finally crystallizing into 2D Mo 1−x W x Se 2 alloy.…”

“…To begin with, MBE is easily scalable and versatile for the growth of various 2DLM alloys. Thus far, it has been successfully exploited to synthesize 2D (Bi 1−x Sb x ) 2 Te 3 , [171] (Bi 1−x Sb x ) 2 Se 3 , [172] GaTe x Se 1−x , [173] WSe 2−x Te x , [174] Mo x W 1−x Se 2 , [170] V x Mo 1−x Se 2 , [175] and As x Te 1−x [176] alloys. In addition, by virtue of the precisely modulated supply rate of the molecular beam flux, the thickness of MBE-grown 2DLMs can be readily controlled.…”

“…The top and bottom insets show the corresponding selected area electron diffraction patterns from the (Bi 1−x Sb x ) 2 Se 3 and substrate, respectively. c) Angle-resolved photoemission spectroscopy images of the (Bi 1−x Sb x ) 2 Se 3 alloys for x = 0 c a ), 0.25 c b ), 0.45 c c ), 0.7 c d ) [172]. b,c) Reproduced with permission [172].…”

Molecular‐Beam Epitaxy of 3D Topological Insulator Thin Films and Devices on Si Substrates

“…This is also in stark contrast to conventional epitaxy based on covalent bonds, where the covalent bonds cause strained layers for very thin films, which results in a partial relaxation with a concurrent formation of dislocations. Hence, the vdW epitaxy of TI films can be realized on a large variety of substrates, and the MBE growth of fully relaxed TI films has been successfully accomplished on SrTiO 3 , [ 27 ] SiC, [ 12 ] CdS, [ 28 ] CdTe, [ 29,30 ] Al 2 O 3 , [ 31 ] GaAs, [ 32,33 ] GaN, [ 34 ] graphene, [ 12 ] InP, [ 35–37 ] and Si. [ 4,22,38,39,40,41 ] However, most of these substrates have a hexagonal arrangement of the surface atoms, i.e., the (111) orientation for cubic substrates and (0001) orientation for hexagonal substrates, to match the hexagonal crystal structure of the TI material, which is mandatory to warrant single‐crystal growth, as will be discussed in the next paragraph.…”