Bi2Te3

Subscriber access provided by MAHIDOL UNIVERSITY (UniNet)

Article

P-N Junctions in Ultrathin Topological Insulator Sb2Te3 / Bi2Te3 Heterostructures Grown by Molecular Beam Epitaxy Martin Lanius, Jörn Kampmeier, Christian Weyrich, Sebastian Kölling, Melissa Schall, Peter Schüffelgen, Elmar Neumann, Martina Luysberg, Gregor Mussler, Paul M. Koenraad, Thomas Schaepers, and Detlev Grützmacher Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.5b01717 • Publication Date (Web): 16 Mar 2016 Downloaded from http://pubs.acs.org on March 22, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Crystal Growth & Design is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 7

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Crystal Growth & Design

P-N Junctions in Ultrathin Topological Insulator Sb2 Te3 /Bi2 Te3 Heterostructures Grown by Molecular Beam Epitaxy Martin Lanius1 , Jörn Kampmeier1 , Christian Weyrich1 , Sebastian Kölling2 , Melissa Schall1 , Peter Schüffelgen1 , Elmar Neumann1 , Martina Luysberg1 , Gregor Mussler1 , Paul M. Koenraad2 , Thomas Schäpers1 , and Detlev Grützmacher1 1 Peter Grünberg Institut and Jülich Aachen Research Alliance (JARA-FIT), Forschungszentrum Jülich, 52425 Jülich, Germany and 2 Institute for Applied Physics (PSN), Technische Universität Eindhoven, 5600 MB Eindhoven, Netherlands

Abstract

We fabricated topological insulating Sb2 Te3 /Bi2 Te3 p-n heterostructures by means of molecular beam epitaxy and characterized the topography of the films by scanning tunneling microscopy. Due to the van der Waals growth mode of the layered Te compounds, X-ray diffraction measurements show that the heterostructure is fully relaxed on the Si(111) substrate. Furthermore, scanning transmission electron microscopy measurements unveil the crystalline structure of the p-n interface. Energy dispersive X-ray spectroscopy and atom probe tomography enable the mapping of the chemical element distribution. We conclude that a diffusion of Sb and Bi during growth causes the formation of ternary compounds. In addition a Sb and Te accumulation at the substrate interface could be detected. Transport measurements prove the tunability of the carrier concentration via thickness variation of the p-n heterostructure.

junction formed by a p-doped topological insulator layer on top of an n-doped one [11]. The underlying idea is that the space charge layer formed at the interface reduces the carrier concentration in the system and by that allows transport in the topologically protected surface states only. Moreover, variation of the thickness of both layers is an elegant way to shift the Fermi energy in a customized fashion, which is required, e.g. to realize Majorana quasiparticles for quantum computing applications [12]. The coexistence of a p- and n-doped layer would also be an interesting situation to form a recently proposed exciton condensate [13]. A heterostructure formed by p-doped Sb2 Te3 and ndoped Bi2 Te3 can be regarded as an ideal material combination to realize the p-n junction mentioned above. Apart from fulfilling the required doping conditions, their van der Waals growth mode [14] makes it possible to fabricate relaxed TI films on Te-passivated high lattice mismatched substrates [15]. Both TI grow in a sequence of five atomic layers Te-X-Te-X-Te (X = Bi or Sb), which is called quintuple layer (QL) [16]. The characteristic height of a quintuple layer is d ⇡ 1 nm. With respect to the fabrication of electronic devices, Si(111) with its high crystalline quality and hexagonal surface is a suitable substrate for these p-n junctions. In order to achieve a well determined interface and extremely smooth surfaces, molecular beam epitaxy (MBE) is a well-suited technique. In this paper we report on the MBE growth of Sb2 Te3 /Bi2 Te3 p-n junctions on Si(111) substrate with varying thicknesses, focussing on the growth and transport properties of the films. Angle resolved photoelectron spectroscopy (ARPES) measurements and a detailed simulation of these junctions are presented elsewhere [17]. In situ scanning tunneling microscopy (STM) measurements were used to characterize the topography of the TI heterostructures in order to determine differences in the growth mode to Sb2 Te3 and Bi2 Te3 on a Si(111) sub-

Introduction

Triggered by the promise of dissipationless surface transport, three-dimensional topological insulators (TI) attracted a lot of attention in applied as well as in basic physics [1]. The current-carrying surface states are topologically protected by time reversal symmetry, i.e. the spin orientation is locked to the direction of motion. This specific property makes topological insulators particularly interesting for spintronics as well as for quantum computation [1, 2]. Especially with respect to the latter, the formation of Majorana quasiparticles at the interface between a superconductor and a topological insulator would offer a very robust and versatile computation scheme. Band structure calculations showed that Sb2 Te3 , Bi2 Se3 , and Bi2 Te3 are very promising materials to realize a three-dimensional topological insulator [3]. However, it was found out experimentally that all these materials have a relatively large background doping (n3D ⇠ 1019 cm 3 ) caused by vacancies or anti-site defects [4, 5], i.e. Sb2 Te3 is found to be p-type, while Bi2 Te3 is n-type [6, 7]. More severely, the background doping pushes the Fermi level out of the band gap region into the bulk valence or conduction band for por n-type doping, respectively. As a consequence, the transport is mainly carried by bulk carriers instead of carriers within the topologically protected surface states. In order to have access to the exceptional properties of topological insulators, it is mandatory to move the Fermi level into the band gap region. One viable approach is to use ternary [8] or quaternary [9, 10] compounds, e.g. (Bix Sb1 x )2 Te3 , and make use of a compensation between p- and n-type doping. However, it is difficult to obtain a precise composition and a homogeneous distribution of elements for epitaxially grown topological insulators. Here, we follow a different approach, rather than employing ternary or quaternary materials we realized a p-n 1

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

strate [18]. Scanning transmission electron microscopy (STEM) high-angle annular dark field (HAADF) images reveal the quality of the crystalline film. Energy dispersive X-ray spectroscopy (EDX) is utilized to determine the chemical distribution of Sb, Bi, and Te on a nanometer scale. To determine the chemical composition of the film and the interface to the substrate, atom probe tomography (APT) measurements were carried out. This knowledge is essential for understanding the growth process and the origin of band structure variations. Furthermore, transport measurements were performed at low temperatures to determine the impact of the junction on the bulk carrier concentration.

Page 2 of 7

from the films via photolithography and ion beam etching. The Hall bars had a length of 600 µm and widths of 20 60 µm. All measurements were performed using a four-point setup with 150 300 µm contact separation. Results and discussion

Figure 1a shows a STM image of an ultrathin heterostructure of 1.5 nm Sb2 Te3 on top of 3 nm Bi2 Te3 . In comparison to previous measurements [18], the p-n junction shows a similar surface structure like thin Bi2 Te3 films. The ultrathin film of Sb2 Te3 grows in a layer-bylayer mode, showing a higher mobility than by growing on the vicinal Si(111) surface. These layers are intersected by 0.4 nm step edges (dashed lines in Fig. 1a), consisting of a Sb-Te sub-quintuple layer, which are caused by the Si(111) substrate steps. The resulting roughness of the film is the minimum for films grown on Si(111) and could only be improved by a substrate with a lower miscut.

Experimental details

100 mm Si(111) wafers were cleaned by a RCA-HF last procedure to remove organic contaminations and the native oxide. A HF dip passivates the Si surfaces with hydrogen during the ex situ transfer from cleanroom into the MBE growth chamber (base pressure p s 1 · 10 9 mbar). To desorb the hydrogen adatoms from the surface the samples were heated up to 700 °C for 10 min and then cooled down to 300 °C. To start the growth process the substrate had been flushed with Te for several seconds before the Bi evaporator was opened. For the evaporation of Bi, Te, and Sb standard effusion cells were heated to TSb = 450 °C, TTe = 330 °C, and TBi = 480 °C. To compose the p-n junction, first a film of Bi2 Te3 was deposited on the silicon substrate, while the Sb-evaporator was heated up in parallel. For the growth of Sb2 Te3 on top, the Bi shutter was closed and Sb was opened simultaneously, while Te was kept open. After growth, the samples were transferred under UHV conditions into a STM chamber [19]. Ex situ X-ray reflectivity and X-ray diffraction measurements were performed by means of a triple-axis Bruker D8 diffractometer to determine the thickness and crystalline quality of the films. For STEM images an aberration corrected FEI Titan G2 80-300 microscope with a Bruker 4-quadrant EDX detector was utilized. The samples for STEM measurements were fabricated in a FEI Helios Nanolab dualbeam FIB (focused ion beam) system and thinned by a Fishione Nanomill with Ar-ions. For APT several conical tips were prepared by FIB and capped with Cr. The diameter of the samples was between 25 nm and 100 nm. The analyses were performed in a Cameca LEAP 4000X HR. For the measurement the samples were cooled down to T = 20 K in UHV and were eveporated by a combination of standing high voltage and a laser with a wavelength = 355 nm. The pulse frequency was f = 65 kHz and the pulse energy was in the order of E = 4 pJ. The evaporated atoms and atom clusters were detected in a mass spectrometer. Transport measurements were performed at T = 1.5 K in a 4 He cryostat equipped with a magnetic field of up to B = 14 T. A DC current of I = 50 µA was applied to the Hall bars patterned

Fig. 1: a) STM image of 1.5 nm Sb2 Te3 on top of a 3 nm Bi2 Te3 layer. Step heights are given in quintuple layers (QL) relative to the plane denoted “0”. b) STM image of 4 nm Sb2 Te3 on 4 nm Bi2 Te3 . Dashed lines (a) and black arrows (b) mark the 0.4 QL steps originating from the Si(111) substrate step edges. c) XRD patterns of heterostructures with increasing Sb2 Te3 thickness: 6.6 nm (black), 7.5 nm (blue), 15.5 nm (green) and 25.5 nm (red), indicating a good crystalline quality of all grown heterostructures.

For a film of 4 nm Sb2 Te3 on 4 nm Bi2 Te3 (Fig. 1b) the growth mechanism changes from a nearly perfect layer-by-layer to a mound formation on a closed multilayer film, which is known for thicker TI films [15]. The Sb2 Te3 seems to adopt the properties of Bi2 Te3 film and shows also substrate induced sub-layers of 0.4 nm 2


Page 3 of 7

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


in height (marked with black arrows in Fig. 1b), which do not influence the formation of mounds. These substrate steps propagate through the whole TI film [18] and generate stacking defects similar to an antiphase boundary. XRD measurements of several heterostructures with varying Sb2 Te3 and constant Bi2 Te3 thickness are presented in Fig. 1c. For all heterostructures the characteristic reflections of Bi2 Te3 and Sb2 Te3 are found. The calculated values for the lattice constants of both materials indicate a fully relaxed growth and a high crystalline quality of the films. We conclude that the interface between Bi2 Te3 and Sb2 Te3 has no detrimental influence on the growth mode of the Sb2 Te3 film. To reveal the interfacial structure a 15 nm Sb2 Te3 film on 6 nm Bi2 Te3 was investigated by high-resolution STEM. Figure 2a displays a bright-field image, where the interface between Si substrate and Bi2 Te3 is seen to be of high crystalline perfection, i.e. no structural defects or amorphous layers are revealed. In the corresponding high-angle annular dark-field image (Fig. 2b) contrast scales with the atomic number squared (and with specimen thickness), which causes Si appearing darkest and Bi atomic columns (red arrows) brightest. As Sb and Te exhibit almost the same atomic number, no contrast difference is reavealed between Te (green arrows) and Sb (blue arrows) layers. Across the whole image individual quintuple layers can be clearly identified by dark contrast lines at the position of the van der Waals gaps.

at least 50 nm. At the interface between both films a gradient of contrast is observed over several nanometers. We can conclude that there is a number of intermixed quintuple layers, where both Bi and Sb are incorporated in the layer of the TI. To measure a profile of the concentration of each element, EDX spectroscopy was performed. For Bi the L↵ line (EBi = 10.837 keV) and for Sb and Te the K↵ -lines (ESb = 26.359 keV and ETe = 27.471 keV) were choosen for quantification.

Fig. 3: a) Line profile of the calculated mass percentage from the EDX signal of the heterostructure in correlation to the distance from the surface and the corresponding dark-field image. The maxima of the Bi and Sb EDX signal correspond to the quintuple layers in the dark-field (DF) image, while the Te maxima match to the Te-Te vdW gaps between the quintuple layers. Below the linescan a scheme of the heterostructure are displayed. The regions close to the interface to the substrate and to the Pt protection layer are excluded in the EDX calculation due to possible preparation artifacts. The linescan is rotated through 90° with respect to the presented images shown in Fig. 2. b) Normalized line profile of the gradient regime (black rectangle in Fig. 3a).

Fig. 2: STEM bright-field (a) and dark-field (b) images of 15 nm Sb2 Te3 on 6 nm Bi2 Te3 . The interface to the Si substrate showing bright contrast in a) is perfectly crystalline. The Bi2 Te3 layer is identified by bright atom positions in b). Some of the Bi, Sb, and Te layers are marked with red, blue, and green arrows, respectively.

Figure 3a displays the line profile of the element distribution in mass percentage received from the analysis of the EDX spectra. The local maxima correspond to the individual atomic layers. This is clearly seen e.g. within Bi2 Te3 where the maxima of the Bi signal coincide with the minima of the Te signal. The maxima of the Te signal fit perfectly to the Te-Te vdW gaps in the corresponding DF image in Fig. 3a, while the maxima of the Bi sig-

It is well known that X2 Te3 compounds nucleate in two different domains on Si(111) [20]. However, in Fig. 2 only one domain is present, indicating domain sizes of 3



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 7

nal fit to the quintuple layers. A similar coherence can be found for Sb and Te in the Sb2 Te3 film. The profile indicates an interdiffusion of Bi (red) and of Sb (blue), causing a concentration gradient at the interface of the heterostructure. By normalizing the Sb and Bi curves (Fig. 3b), the width of the diffused interface could be determined to be d t 4 nm. In this region the concentration of either Bi or Sb drops from 80% to 20%. The Te content (green) is, as expected, nearly constant in the complete heterostructure, indicating a diffusion only between Sb and Bi lattice positions. Farther away from the interface neither the Bi nor the Sb concentration drops to zero. Hence, ternary compounds are grown rather than pure constituents. These regions are displayed in the scheme of Fig. 3a as (Bix Sb1 x )2 Te3 and (Biy Sb1 y )2 Te3 .

Fig. 4: a) 2D projection of the 3D ion map measured by the APT showing the reconstructed positions of the ions and clusters of 15 nm Sb2 Te3 film on 6 nm Bi2 Te3 . b) Quantified 1D concentration profile of the heterostructure presented in a). The length scale of the profile was adjusted by the STEM images. Black arrows in both images mark the Sb and Te accumulation at the Si interface.

Figure 4b shows the quantified profile of the heterostructure. In this representation the signal of clusters of SbTe and BiTe is distributed to the respective elements, counting once for both contained elements, in order to obtain absolute values for the concentration of each element. Because the APT yields no exact information about the thickness of the measured film, the curve was adjusted to the length scale of the STEM measurements. The atom concentration in the bulk of the p-n junction amounts to x t 0.1 and y t 0.6 for the Bi content of the ternary compounds defined in Fig. 3. Furthermore, the width of the interface between both TIs is around d t 4 nm, which is in perfect agreement with the EDX measurement. The Te content (green curve in Fig. 4a) is constant over the whole heterostructure, indicating diffusion only between Sb and Bi lattice positions. In the region of the first layer at the interface to the Si(111) substrate, the Sb and Te concentrations rise along with the Si concentration, while the Bi signal decreases nearly to zero (black arrows in Fig. 3). The Te excess can be partly explained by the Te-passivation layer at the Si substrate. The STEM, EDX and APT measurements can be summarized to two results: First, there is a diffusive interface between Sb2 Te3 and Bi2 Te3 and non-vanishing concentrations of Bi in Sb2 Te3 and Sb in Bi2 Te3 , respectively. The resulting formation of two ternary compounds

To determine the absolute values for the concentration of both layers, we performed atom probe tomography (APT) measurements. Figure 4a represents a 2dimensional projection of the 3-dimensional ion map of the same Sb2 Te3 /Bi2 Te3 heterostructure measured by STEM and EDX. The map shows the main isotopes of each element and clusters of SbTe and BiTe are displayed to give a qualitative image of the element distribution. The interdiffusion between the Sb2 Te3 and the Bi2 Te3 film and the formation of ternary compounds is clearly visible. At the interface to the Si substrate an accumulation of Sb and Te of less than d t 1 nm can be identified. A diffusion deeper into the substrate of one of the elements of the heterostructure can be excluded. 4


Page 5 of 7

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


could cause a shifting of the Fermi energy in the particular p- and n-doped part of the heterostructure. This would effectuate a lower band-bending at the interface in comparison to a theoretical model of a pure Sb2 Te3 /Bi2 Te3 structure without diffusion. We assume that the high temperature during growth causes the interdiffusion. Second, at the interface to the substrate the Sb and Te concentrations rise, while the Bi concentration reaches zero. The Sb-rich accumulation has a thickness of around d t 1 nm and coexists with a significant Si concentration. This could lead to a p-doped layer at the Si interface and maybe also dope the surface of the substrate as Sb is a well known n-type dopant in Si. Additionally, magnetotransport measurements were performed in a cryostat at T = 1.5 K with magnetic fields up to B = 14 T. The results are shown in Fig. 5. Here, different films with varying thicknesses were investigated. For all films the Bi2 Te3 layer was kept constant at 6 nm according to the STEM measurement, while the thickness of the Sb2 Te3 was increased. The total film thicknesses were measured using a surface profiler.

port, respectively. It appears to be an optimal thickness relation between the Bi2 Te3 and Sb2 Te3 layers tending towards a slightly thicker Sb2 Te3 component compared to the Bi2 Te3 . This could be linked to the fact that unintentionally doped binary Sb2 Te3 films usually have a carrier concentration lower than Bi2 Te3 by a factor of roughly 1.6 7.5, which is possibly related to a smaller amount of point defects in MBE-grown Sb2 Te3 with respect to MBE-grown Bi2 Te3 . Considering that the Bi2 Te3 has a thickness of 6 nm, this would correspond to 9.6 45 nm thick Sb2 Te3 or total film thickness d = 15.6 51 nm. Nevertheless, the absolute carrier concentration values of the Sb2 Te3 /Bi2 Te3 heterostructures are not significantly lower in comparison to pure Bi2 Te3 (n2D = 1.1 3.3 · 1014 cm 2 ) or Sb2 Te3 (p2D = 0.44 0.67 · 1014 cm 2 ) grown in this system. Alloys of (Bix Sb1 x )2 Te3 grown by MBE show similar carrier concentrations (n2D = p2D ⇠ 1014 cm 2 ) and the lowest reported values are in the range of n2D ⇠ 1013 cm 2 [21], which have not been reached in our Sb2 Te3 /Bi2 Te3 heterostructures so far. However, all Hall measurements on the heterostructures display a clear nonlinearity (not shown) as opposed to the strictly linear Hall responses of the binary systems. This indicates multiple transport channels, most likely connected to the Bi2 Te3 and Sb2 Te3 dominated layers of the heterostructure, where no carrier compensation occurs. Furthermore, the Sb and Te accumulation at the interface to the substrate could dope the Si and could create an additional transport channel. The dependencies of both carrier concentration and sheet resistance on the thicknesses of Bi2 Te3 and Sb2 Te3 indicate, that the carrier depletion can be controlled via the thickness of the heterostructure.

Summary

In conclusion we have grown a heteroepitaxial p-n junction of Bi2 Te3 and Sb2 Te3 with the ability to tune the carrier concentration and doping character via thickness variation. Characterisation via STM shows a flat surface with Sb2 Te3 adopting the properties of the underlying Bi2 Te3 film. STEM and XRD measurements demonstrate a high crystalline quality of the heterostructure and a van der Waals growth without strain or interface defects. EDX measurements show diffusion of Sb and Bi, therefore the heterostructure is composed out of several ternary compounds. The values for the concentrations of Sb and Bi were determined by APT. A depth profile of the heterostructure revealed a Sb accumulation at the interface to the Si(111) substrate, creating a additional possible p-doped layer. The transport measurements reveal the tunability of the intrinsic carrier concentration by changing the film thickness of Bi2 Te3 or Sb2 Te3 . Future experiments are dedicated to a further decrease in carrier concentration by changing the n-doped TI of the junction to a different material or extend to more complex superlattice structures.

Fig. 5: a) 2D charge carrier density and b) sheet resistance in dependence of the film thickness. The thickness of the Sb2 Te3 was varied, while the thickness of Bi2 Te3 was kept constant at 6 nm.

As can be seen in Fig. 5a, the dominant carrier change from electrons in the two thinner films to holes in the thicker ones. When the Sb2 Te3 thickness is increased, the sheet resistance rises at first, but falls off again beyond a critical value (Fig. 5b). Obviously, the expected maximum in sheet resistance falls into the same range of film thickness as the projected minimum in carrier concentration and the change from n- to p-type trans5



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 7

Institute for Topological Insulators (VITI).

Acknowledgements

The authors acknowledge financial support from the priority programme SPP1666 and the Helmholtz Virtual

[1] J. E. Moore, Nature 464, 194, 2010. [2] W-J. Shan, H-Z. Lu, and S-Q. Chen, New Journ. of Phys. 12, 043048, 2010. [3] H. Zhang, C-X. Liu, X-L. Qi, X. Dai, Z. Fang, and S-C. Zhang, Nature Phys. 5, 438-442, 2009 [4] D. O. Scanlon, P. D. C. King, R. P. Singh, A. de la Torre, S. McKeown Walker, G. Balakrishnan, F. Baumberger, and C. R. A. Catlow. Adv. Mat., 24, 2154-2158, 2012. [5] P. Lostak, Z. Stary, J. Horak, and J. Pancir. Phys. Stat. Sol. (a), 115, 87, 1989. [6] Y. Xia, L. Wray, D. Qian, D. Hsieh, A. Pal, H. Lin, A. Bansil, D. Grauer, Y. Hor, R. Cava, and M. Hasan, Nature Phys. 5, 398-402, 2009. [7] D. Hsieh, Y. Xia, D. Quian, L. Wray, F. Meier, J. H. Dil, J. Osterwalder, L. Patthey, A. V. Fedorov, H. Lin, A. Bansil, D. Grauer, Y. Hor, R. Cava, and M. Hasan, Phys. Rev. Lett. 103, 2009. [8] J. Zhang, C. Chang, Z. Zhang, J. Wen, X. Feng, M. Liu, K. He, L. Wang, X. Chen, Q. Xue, X. Ma, and Y. Wang, Nature Comm. 2, 574, 2011. [9] Y. Xu, I. Miotkowski, C. Liu, J. Tian, H. Nam, N. Alidoust, J. Hu, C-K. Shih, M. Z. Hasan, and Y. P. Chen, Nature. 10, 956-962, 2014. [10] T. Arakane, T. Sato, S. Souma, K. Kosaka, K. Nakayama, M. Komatsu, T. Takahashi, Z. Ren, K. Segawa, and Y. Ando, Nature Comm. 3, 636, 2012. [11] J. Wang, X. Chen, B. F. Zhu, and S. C. Zhang, Phys. Rev. B, 85, 2012.

[12] L. Fu and C. Kane, Phys. Rev. Lett. 100, 2008. [13] B. Seradjeh, J. Moore, and M. Franz, Phys. Rev. Lett. 103, 2009. [14] A. Koma, Thin Solid Films 72, 216, 1992. [15] S. Borisova, J. Krumrain, M. Luysberg, G. Mussler, and D. Grützmacher, Cryst. Growth. a. Design 12, 60986103, 2012. [16] H. Zhang, C-X. Liu, X-L Qi, Z. Fang, and S-C. Zhang, Nature Phys. 5, 438, 2009. [17] M. Eschbach, E. Mlynczak, J. Kellner, J. Kampmeier, M. Lanius, E. Neumann, C. Weyrich. M. Gehlmann, P. Gospodaric, S. Döring, G. Mussler, N. Demarina, M. Luysberg, G. Bihlmayer, T. Schäpers, L. Plucinski, M. Morgenstern, S. Blügel, C. M. Schneider, and D. Grützmacher, Nature Comm. 6, 8816, 2015. [18] S. Borisova, J. Kampmeier, M. Luysberg, G. Mussler, and D. Grützmacher, App. Phys. Lett. 103, 081902, 2013. [19] O. Leifeld, B. Müller, D. Grützmacher, and K. Kern, App. Phys. A. 66, 993-997, 1998. [20] J. Kampmeier, S. Borisova, L. Plucinski, M. Luysberg, G. Mussler, and D. Grützmacher, Cryst. Growth. a. Design 15, 390-394, 2015 [21] C. Weyrich, M. Drögeler, J. Kampmeier, G. Mussler, T. Merzenich, T. Stoica, I. E. Batov, J. Schubert, L. Plucinski, B. Beschoten, C. M. Schneider, D. Grützmacher, and T. Schäpers, arXiv, 1511.00965v2. 2015.

6


Page 7 of 7

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


For Table of Contents Use Only Manuscript title: P-N Junctions in Ultrathin Topological Insulator Sb2Te3 /Bi2Te3 Heterostructures Grown by Molecular Beam Epitaxy Author List: Martin Lanius, Jörn Kampmeier, Christian Weyrich, Sebastian Kölling, Melissa Schall, Peter Schüffelgen, Elmar Neumann, Martina Luysberg, Gregor Mussler, Paul M. Koenraad, Thomas Schäpers, Detlev Grützmacher TOC graphics:

Synopsis: Carrier concentration is tuned in n-Bi2Te3/p-Sb2Te3 topological insulator stacks by thickness variation. Surface morphology of Sb2Te3 adopts properties of underlying Bi2Te3 film. Bi-Sb interdiffusion takes place at the Bi2Te3/Sb2Te3 interface.


Bi2Te3

Recommend Documents