Toward the Intrinsic Limit of the Topological InsulatorBi2Se3

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.

Chiral Spin Mode on the Surface of a Topological Insulator

“…As-grown Bi 2 Se 3 is usually electron-doped due to naturally formed Se vacancies [48]. In this study, we use well-characterized samples with low concentration of impurities and crystalline defects [49]. All the bulk phonon modes in this crystal are sharp with no signatures of any impurity modes, and all the surface phonon modes are clearly observed [50].…”

Nanoimaging of Electronic Heterogeneity in Bi2Se3 and Sb2Te3 Nanocrystals

“…For Bi 2 Se 3 , the most common defect is Se deficiency. [9] However, the EDX elemental mapping shows that Se and Bi are uniformly distributed within the detection limit of ≈0.5 wt% ( Figure S6, Supporting Information). Even in nano-Auger element mapping ( Figure S7, Supporting Information) with a lower detection limit (≈0.1 at%) and a higher lateral resolution (≈10 nm), the distribution of Se also appears to be uniform.…”

“…[9,19] However, these previous studies only focus on the identification of defects at the atomic level, without probing the distribution of these defects at the mesoscopic scale, and the associated influence on the electronic structures and optical properties. Herein, our IR s-SNOM images reveal that these defect-rich regions, with higher carrier concentrations, can form mesoscale optical contrast with high symmetry, and these optical responses can be understood and simulated by a simple theoretical model (Figure 2h).…”

“…[9,[19][20][21] However, STM is limited to conducting substrates and typically cannot access heterogeneity that spans the multiple atomic-to-mesoscopic length scales. Infrared scatteringtype scanning near-field optical microscopy (IR s-SNOM), in contrast, based on an atomic force microscope (AFM) coupled with a tip-localized optical excitation, can probe the low-energy local electronic structure associated with the Drude response with 10 nm resolution, and over multiple length scales with exquisite sensitivity.…”

“…The associated unique electronic structure of the helical Dirac surface states results in many exotic physical properties, such as the topological magneto-electric effect, [6] Majorana fermions, [7] and the quantum anomalous Hall effect. [8] However, because of the low formation energy of intrinsic defects, [9] the resulting bulk conductivity often obscures or even suppresses the desired TI behavior. [10][11][12] The realization of these novel topological phases requires high-quality TI thin films with sufficiently low defect concentration, typically obtained by molecular beam epitaxy growth.…”