Suppressing Twin Formation in Bi<sub>2</sub>Se<sub>3</sub> Thin Films

Tarakina, Nadezda V.; Schreyeck, S.; Luysberg, M.; Grauer, S.; Schumacher, C.; Karczewski, G.; Βrunner, Karl; Gould, C.; Buhmann, H.; Dunin-Borkowski, Rafal E.; Molenkamp, L. W.

doi:10.1002/admi.201400134

Cited by 59 publications

(80 citation statements)

References 33 publications

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“…Note that the InP (113) plane occurs at the same φ azimuthal angle as the (002) plane referred to in Ref. 8. We also observe that a partial suppression of twinning can also occur on sapphire substrates, despite a larger lattice mismatch, as shown in Fig.…”

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Characterizing the structure of topological insulator thin films

et al. 2015

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We describe the characterization of structural defects that occur during molecular beam epitaxy of topological insulator thin films on commonly used substrates. Twinned domains are ubiquitous but can be reduced by growth on smooth InP (111)A substrates, depending on details of the oxide desorption. Even with a low density of twins, the lattice mismatch between (Bi,Sb) 2 Te 3 and InP can cause tilts in the film with respect to the substrate. We also briefly discuss transport in simultaneously top and back electrically gated devices using SrTiO 3 and the use of capping layers to protect topological insulator films from oxidation and exposure.

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“…Some typical substrates commonly used are GaAs (111), InP (111), sapphire, Si (111), and SrTiO 3 (STO) (111), among others. [5][6][7][8][9][10][11][12][13][14] These films grow c-axis oriented out of plane, using the typical hexagonal indexing scheme where the (0 0 n) reflections are along the (111) direction if the rhombohedral unit cell was used instead.…”

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Characterizing the structure of topological insulator thin films

et al. 2015

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“…The influence of the interfaces between the layer and the sub-strate, as well as between the layer and either an AlO x or Te cap layer applied for surface protection on magnetotransport studies revealing the QAHE is still not clear. A high structural quality of the layers has been claimed to be a prerequisite of QAHE, while epitaxial tetradymite layers in general suffer from rotational twinning, translational domain boundaries, screw dislocations and quintuple layer (QL) surface steps [16,17]. The coincidence of the QAHE and contributions of superparamagnetic phases observed in magnetotransport in the nominally ferromagnetic phase of such layers as well as a multidomain network during the magnetization reversal process suggest that the layers are inhomogeneous in magnetic as well as structural properties [11,18].…”

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“…• C in Te atmosphere in order to clean and smoothen the surface and subsequently cooled to a given T s [17]. The beam equivalent pressure (BEP) of molecular beams is measured by a Bayard Alpert ion gauge at the substrate position.…”

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Epitaxy and structural properties of (V,Bi,Sb) 2Te3 layers exhibiting the quantum anomalous Hall effect

Winnerlein

Schreyeck

Grauer

et al. 2017

Phys. Rev. Materials

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The influence of Sb content, substrate type and cap layers on the quantum anomalous Hall effect observed in V-doped (Bi,Sb)2Te3 magnetic topological insulators is investigated. Thin layers showing excellent quantization are reproducibly deposited by molecular beam epitaxy at growth conditions effecting a compromise between controlled layer properties and high crystalline quality. The Sb content can be reliably determined from the in-plane lattice constant measured by X-ray diffraction, even in thin layers. This is the main layer parameter to be optimized in order to approach charge neutrality. Within a narrow range at about 80% Sb content, the Hall resistivity shows a maximum of about 10 kΩ at 4 K and quantizes at mK temperatures. Under these conditions, thin layers grown on Si(111) or InP(111) and with or without a Te cap exhibit quantization. The quantization persists independently of the interfaces between cap, layer and substrate, the limited crystalline quality, and the degradation of the layer proving the robustness of the quantum anomalous Hall effect.A quantum anomalous Hall effect (QAHE), in which a Hall plateau with a resistance of h/e 2 can be observed even in the absence of a magnetic field, was predicted to occur in ferromagnetically doped topological insulators (TIs) [1][2][3][4]. The effect was first observed in 2013 in a 5 nm Cr 0.15 (Bi 0.1 Sb 0.9 ) 1.85 Te 3 layer without a cap layer, and grown on a SrTiO 3 substrate [5]. The QAHE has since been reproduced in such tetradymite-type layers with different layer thicknesses, layer compositions, magnetic dopants (Cr or V), with/without a cap layer and on various substrates [6][7][8][9][10][11]. Perfect quantization was observed in Cr-doped (Bi,Sb) 2 Te 3 layers capped by an AlO x layer on GaAs substrates, and V-doped (Bi,Sb) 2 Te 3 layers capped by Te on SrTiO 3 substrates and Si(111) substrates [6,[9][10][11]. Many authors point out that the layer properties have to be optimized to observe the QAHE, but details of the epitaxial growth conditions, the structural layer properties and the applied characterization techniques are sparse.An apparent requirement for observing the QAHE is the optimization of Sb content in order to approach charge neutrality by compensation of n-and p-type intrinsic point defects. Further, an applied gate bias is needed to tune the Fermi level into the bandgap of topological surface states (TSSs) caused by magnetization [5]. The layer thickness, ranging from about 4 to 10 nm in the literature, likely affects the hybridization of the TSSs and possibly also the mechanisms leading to the QAHE. Theoretical predictions and experiments both reveal a degradation of the surface states due to oxidation in Bi 2 Te 3 layers and shifts of the Fermi level in epitaxial tetradymite layers due to adsorbates [12][13][14][15]. The influence of the interfaces between the layer and the sub- * M. Winnerlein and S. Schreyeck contributed equally to this work.† Karl.Brunner@physik.uni-wuerzburg.de strate, as well as between the layer and either an...

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