Toward the Intrinsic Limit of the Topological Insulator ${\mathrm{Bi}}_{2}{\mathrm{Se}}_{3}$

Toward the Intrinsic Limit of the Topological Insulator ${Bi}_{2} {Se}_{3}$

Jixia Dai, Damien West, Xueyun Wang, Yazhong Wang, Daniel Kwok, S.-W. Cheong, S. B. Zhang, and Weida Wu

Phys. Rev. Lett. 117, 106401 – Published 29 August 2016

Abstract

Combining high resolution scanning tunneling microscopy and first principles calculations, we identified the major native defects, in particular the Se vacancies and Se interstitial defects, that are responsible for the bulk conduction and nanoscale potential fluctuations in single crystals of archetypal topological insulator ${Bi}_{2} {Se}_{3}$ . Here it is established that the defect concentrations in ${Bi}_{2} {Se}_{3}$ are far above the thermodynamic limit, and that the growth kinetics dominate the observed defect concentrations. Furthermore, through careful control of the synthesis, our tunneling spectroscopy suggests that our best samples are approaching the intrinsic limit with the Fermi level inside the band gap without introducing extrinsic dopants.

Received 8 November 2015

DOI:https://doi.org/10.1103/PhysRevLett.117.106401

Physics Subject Headings (PhySH)

Defects Topological insulators

Chalcogenides

First-principles calculations Scanning tunneling microscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Jixia Dai¹, Damien West^2,*, Xueyun Wang¹, Yazhong Wang¹, Daniel Kwok¹, S.-W. Cheong¹, S. B. Zhang², and Weida Wu^1,†

¹Rutger-Center for Emergent Materials and Department of Physics and Astronomy, Rutgers University, Piscataway New Jersey 08854, USA
²Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180-3590, USA

^*Corresponding author. damienwest@gmail.com
^†Corresponding author. wdwu@physics.rutgers.edu

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Vol. 117, Iss. 10 — 2 September 2016

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Figure 1
(a) Atomically resolved STM image of (001) surface of nominal ${Bi}_{2} {Se}_{3}$ . Tunneling parameter is $U = - 0.7 V$ , $I = 0.2 nA$ . Green circle, triangle, and squares mark a $V_{Se}$ at the 1A, 3C, and 5B sites, respectively. The blue circle and square mark a ${Bi}_{Se}$ antisite at the 1A and 6C sites. The black square marks a triangular defect (Se interstitial defect) at the A site. See Fig. 2 for details. (b) Cartoon of the triangular lattice and definition of the A, B, and C sites. (c) Definition of atomic sites (1A, 2B, 3C, etc.) in the crystal structure of ${Bi}_{2} {Se}_{3}$ . (d) STS spectrum of nominal ${Bi}_{2} {Se}_{3}$ . The Dirac point energy ( $E_{D}$ ) is $\sim - 340 meV$ .
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Figure 2
Experimental (left) simulated (right) STM images of native defects in ${Bi}_{2} {Se}_{3}$ . (a), (b), and (c) STM images (left) of $V_{Se}$ at 1A, 3C, and 5B sites measured with $- 0.7 V$ , and the corresponding simulations (right). (d), (e), and (f) STM images (left) of ${Bi}_{Se}$ antisites at 1A, 5B, and 6C sites measured with $- 0.6 V$ and the corresponding simulations. (g) and (h) Left: STM images of an intercalated Se defect at $- 0.7$ and $+ 0.5 V$ , respectively; Right: corresponding simulated STM images. The color scale of experimental STM images is 35 pm for (a)–(c), (e)–(h), and 200 pm for (d). The color in the simulated images represents the height of a constant isosurface of charge density, $0.0035 e Å^{- 3}$ . The color scales of the simulated images are the same as that of the experimental images. The absolute distance from the surface for the minimum of the scale is 4.1, 4.4, 4.4, 3.4, 4.6, 4.4, 3.9, and 4.7 Å for (a)–(h), respectively.
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Figure 3
(a) STM topography image of ${Bi}_{2} {Se}_{3}$ showing randomly distributed $V_{Se}$ defects. (b) Dirac point energy ( $E_{D}$ ) map of the same location as a. Black dots are the positions of $V_{Se}$ defects in (a). There is a clear positive correlation between local $V_{Se}$ defect density and local $E_{D}$ . (c) Local conduction ( $d I / d V$ ) map at $- 500 meV$ showing the local potential fluctuation. (d) Simulated defect influence map due to $V_{Se}$ [38].
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Figure 4
(a) and (b) Cartoons of $E_{F}$ relative to band structure in the typical or best ${Bi}_{2} {Se}_{3}$ samples. (c) A summary diagram ( $n$ vs $E_{D}$ ) of various ${Bi}_{2} {Se}_{3}$ crystals with various synthesis conditions. Assuming $V_{Se}$ and ${Se}_{i}$ are donors, the cyan line shows the electron density estimated from parabolic band ( $m * \approx 0.15 m_{e}$ ) [43]. (d) Typical STM topography of sample with extremely low defect density. Inset: corresponding STS showing that $E_{F}$ is below CBM.
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Physical Review Letters

Toward the Intrinsic Limit of the Topological Insulator Bi2Se3

Jixia Dai, Damien West, Xueyun Wang, Yazhong Wang, Daniel Kwok, S.-W. Cheong, S. B. Zhang, and Weida Wu

Phys. Rev. Lett. 117, 106401 – Published 29 August 2016

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Toward the Intrinsic Limit of the Topological Insulator ${Bi}_{2} {Se}_{3}$