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Shekhar P, Bendias K, Fürst L, Liang X, Gbordzoe MK, Borzenko T, Buhmann H, Kleinlein J, Molenkamp LW. Realization of smooth side profile using diffusion-controlled wet chemical etching for HgTe/(Hg,Cd)Te heterostructures. Nanotechnology 2023; 34:205302. [PMID: 36753756 DOI: 10.1088/1361-6528/acba1d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Accepted: 02/08/2023] [Indexed: 06/18/2023]
Abstract
We utilize a diffusion-controlled wet chemical etching technique to fabricate microstructures from two-dimensional HgTe/(Hg,Cd)Te-based topological insulators. For this purpose, we employ a KI: I2: HBr: H2O-based etchant. Investigation of the side profile of the etched heterostructure reveals that HgTe quantum wells protrude from the layer stack as a result of the different etch rates of the layers. This constraint poses challenges for the study of the transport properties of edge channels in HgTe quantum wells. In order to achieve a smoother side profile, we develop a novel approach to the etching process involving the incorporation of a sacrificial design element in the etch mask. This limits the flow of charge carriers to the ions in the electrolyte during the etching process. The simplicity of the method coupled with the promising results achieved thereby should make it possible for the new approach introduced here to be applied to other semiconductor heterostructures.
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Affiliation(s)
- Pragya Shekhar
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Kalle Bendias
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Lena Fürst
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Xianhu Liang
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Michael K Gbordzoe
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Tatiana Borzenko
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Hartmut Buhmann
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Johannes Kleinlein
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
| | - Laurens W Molenkamp
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
- Institute for Topological Insulators, Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany
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Shekhar P, Shamim S, Hartinger S, Schlereth R, Hock V, Buhmann H, Kleinlein J, Molenkamp LW. Low-Temperature Atomic Layer Deposition of Hafnium Oxide for Gating Applications. ACS Appl Mater Interfaces 2022; 14:33960-33967. [PMID: 35820660 DOI: 10.1021/acsami.2c06176] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
We present a novel low-temperature (30 °C) atomic layer deposition process for hafnium oxide and apply the layers as gate dielectric to fabricate devices out of the thermally sensitive topological insulator HgTe. The key to achieving self-limiting growth at these low temperatures is the incorporation of sufficiently long purge times ( ≥150 s) in the deposition cycles. We investigate the structural and compositional properties of these thin films using X-ray reflectometry and photoelectron spectroscopy, finding a growth rate of 1.6 Å per cycle and an atomic ratio of Hf/O of 1:1.85. In addition, we report on the transport properties of the microstructured devices, which are much enhanced compared to previous device generations. We determine a relative permittivity of ∼15 for our HfO2 layers. Our process considerably reduces the thermal load of the samples during microfabrication and can be adapted to a broad range of materials, enabling the fabrication of high-quality gate insulators on various temperature-sensitive materials.
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Affiliation(s)
- Pragya Shekhar
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, 97074 Würzburg, Germany
| | - Saquib Shamim
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, 97074 Würzburg, Germany
| | - Simon Hartinger
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, 97074 Würzburg, Germany
| | - Raimund Schlereth
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, 97074 Würzburg, Germany
| | - Volkmar Hock
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, 97074 Würzburg, Germany
| | - Hartmut Buhmann
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, 97074 Würzburg, Germany
| | - Johannes Kleinlein
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, 97074 Würzburg, Germany
| | - Laurens W Molenkamp
- Physikalisches Institut (EP3), Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
- Institute for Topological Insulators, Am Hubland, 97074 Würzburg, Germany
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Müller VL, Yan Y, Kashuba O, Trauzettel B, Abdelghany M, Kleinlein J, Beugeling W, Buhmann H, Molenkamp LW. Electron-Hole Scattering Limited Transport of Dirac Fermions in a Topological Insulator. Nano Lett 2021; 21:5195-5200. [PMID: 34115500 DOI: 10.1021/acs.nanolett.1c01271] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
We have experimentally investigated the effect of electron temperature on transport in the two-dimensional Dirac surface states of the three-dimensional topological insulator HgTe. We have found that around the minimal conductivity point, where both electrons and holes are present, heating the carriers with a DC current results in a nonmonotonic differential resistance of narrow channels. We have shown that the observed initial increase in resistance can be attributed to electron-hole scattering, while the decrease follows naturally from the change in Fermi energy of the charge carriers. Both effects are governed dominantly by a van Hove singularity in the bulk valence band. The results demonstrate the importance of interband electron-hole scattering in the transport properties of topological insulators.
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Affiliation(s)
- Valentin L Müller
- Institute for Topological Insulators and Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Yuan Yan
- Institute for Topological Insulators and Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Oleksiy Kashuba
- Theoretische Physik IV, Institut für Theoretische Physik und Astrophysik, Universität Würzburg, 97074 Würzburg, Germany
| | - Björn Trauzettel
- Theoretische Physik IV, Institut für Theoretische Physik und Astrophysik, Universität Würzburg, 97074 Würzburg, Germany
| | - Mohamed Abdelghany
- Institute for Topological Insulators and Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Johannes Kleinlein
- Institute for Topological Insulators and Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Wouter Beugeling
- Institute for Topological Insulators and Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Hartmut Buhmann
- Institute for Topological Insulators and Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
| | - Laurens W Molenkamp
- Institute for Topological Insulators and Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
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Shamim S, Beugeling W, Shekhar P, Bendias K, Lunczer L, Kleinlein J, Buhmann H, Molenkamp LW. Quantized spin Hall conductance in a magnetically doped two dimensional topological insulator. Nat Commun 2021; 12:3193. [PMID: 34045456 PMCID: PMC8160016 DOI: 10.1038/s41467-021-23262-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Accepted: 04/21/2021] [Indexed: 11/22/2022] Open
Abstract
Soon after the discovery of the quantum spin Hall effect, it has been predicted that a magnetic impurity in the presence of strong Coulomb interactions will destroy the quantum spin Hall effect. However, the fate of the quantum spin Hall effect in the presence of magnetic impurities has not yet been experimentally investigated. Here, we report the successful experimental demonstration of a quantized spin Hall resistance in HgTe quantum wells dilutely alloyed with magnetic Mn atoms. These quantum wells exhibit an inverted band structure that is very similar to that of the undoped material. Micron sized devices of (Hg,Mn)Te quantum well (in the topological phase) show a quantized spin Hall resistance of h/2e2 at low temperatures and zero magnetic field. At finite temperatures, we observe signatures of the Kondo effect due to interaction between the helical edge channels and magnetic impurities. Our work lays the foundation for future investigations of magnetically doped quantum spin Hall materials towards the realization of chiral Majorana fermions. The quantum spin Hall effect is expected not to survive the presence of magnetic impurities. Here, authors report full quantization at very low temperatures in HgTe quantum wells alloyed with a few percent of magnetic Mn atoms, due to Kondo screening.
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Affiliation(s)
- Saquib Shamim
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, Würzburg, Germany. .,Institute for Topological Insulators, Universität Würzburg, Am Hubland, Würzburg, Germany.
| | - Wouter Beugeling
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, Würzburg, Germany.,Institute for Topological Insulators, Universität Würzburg, Am Hubland, Würzburg, Germany
| | - Pragya Shekhar
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, Würzburg, Germany.,Institute for Topological Insulators, Universität Würzburg, Am Hubland, Würzburg, Germany
| | - Kalle Bendias
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, Würzburg, Germany.,Institute for Topological Insulators, Universität Würzburg, Am Hubland, Würzburg, Germany
| | - Lukas Lunczer
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, Würzburg, Germany.,Institute for Topological Insulators, Universität Würzburg, Am Hubland, Würzburg, Germany
| | - Johannes Kleinlein
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, Würzburg, Germany.,Institute for Topological Insulators, Universität Würzburg, Am Hubland, Würzburg, Germany
| | - Hartmut Buhmann
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, Würzburg, Germany.,Institute for Topological Insulators, Universität Würzburg, Am Hubland, Würzburg, Germany
| | - Laurens W Molenkamp
- Experimentelle Physik III, Physikalisches Institut, Universität Würzburg, Am Hubland, Würzburg, Germany. .,Institute for Topological Insulators, Universität Würzburg, Am Hubland, Würzburg, Germany.
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Bendias K, Shamim S, Herrmann O, Budewitz A, Shekhar P, Leubner P, Kleinlein J, Bocquillon E, Buhmann H, Molenkamp LW. High Mobility HgTe Microstructures for Quantum Spin Hall Studies. Nano Lett 2018; 18:4831-4836. [PMID: 29975844 DOI: 10.1021/acs.nanolett.8b01405] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The topic of two-dimensional topological insulators has blossomed after the first observation of the quantum spin Hall (QSH) effect in HgTe quantum wells. However, studies have been hindered by the relative fragility of the edge states. Their stability has been a subject of both theoretical and experimental investigation in the past decade. Here, we present a new generation of high quality (Cd,Hg)Te/HgTe-structures based on a new chemical etching method. From magnetotransport measurements on macro- and microscopic Hall bars, we extract electron mobilities μ up to about 400 × 103 cm2/(V s), and the mean free path λmfp becomes comparable to the sample dimensions. The Hall bars show quantized spin Hall conductance, which is remarkably stable up to 15 K. The clean and robust edge states allow us to fabricate high quality side-contacted Josephson junctions, which are significant in the context of topological superconductivity. Our results open up new avenues for fundamental research on QSH effect as well as potential applications in spintronics and topological quantum computation.
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Affiliation(s)
- Kalle Bendias
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
| | - Saquib Shamim
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
| | - Oliver Herrmann
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
| | - Andreas Budewitz
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
| | - Pragya Shekhar
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
| | - Philipp Leubner
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
| | - Johannes Kleinlein
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
| | - Erwann Bocquillon
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
- Laboratoire Pierre Aigrain, Ecole Normale Supériere, PSL Research University, Sorbonne Université, Université Paris Diderot, Sorbonne Paris Cité, CNRS , 24 rue Lhomond , 75005 Paris , France
| | - Hartmut Buhmann
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
| | - Laurens W Molenkamp
- Physikalisches Institut (EP3) , Universität Würzburg , Am Hubland, 97074 Würzburg , Germany
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