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Semiconductor Nanowires

In the so-called bottom-up approach semiconductor nanostructures can be formed directly by epitaxial growth. In contrast to the alternative top-down method where lithographical means are used, this approach has the potential to simply the fabrication of low-dimensional semiconductor nanostructures enormously. Among the structures fabricated by the bottom-up approach semiconductor nanowires are particular interesting, since the one-dimensional channel can not only be used as a building block for future nanotransistor but also as a versatile basis for various quantum device structures.   

Our research goal is to use semiconductor nanowires for applications in nano electronics and ultimately for spin-based quantum bits [1]. The semiconductor nanowires are grown either by molecular beam epitaxy (MBE) or by metal-organic vapor phase epitaxy (MOVPE). Regarding the MBE growth a GaAs or Si wafer covered with a thin silicon oxide is used as a substrate, while for the nanowires fabricated by MOVPE selective area growth is employed [2]. In addition to nanowires made of a single material, i.e. InAs or GaAs, our current research focuses on coaxial heterostructures, i.e. core/shell nanowires, which promise a superior carrier confinement.

Nanowire transistor and dotSchematic illustration of a nanowire transistor (left) and quantum dot (right)

MBE and MOVPE InAs nanowireInAs nanowires grown by molecular beam epitaxy (left) and metal-organic vapor phase epitaxy (right)

In order to perform electronic transport measurements the nanowires are transferred to a pre-patterned substrate and contacted by electron-beam lithography defined metallic electrodes. Control of carrier concentration is achieved by a back-gate or by lithographically prepared gate fingers. The latter method allows the definition of quantum dot structures. Most of the transport properties are performed at temperatures below 1 Kelvin, in order to resolve quantum and interference effects. A typical example for interference effects are universal conductance fluctuations which can be used to get information on the electronic phase-coherence length [3-5]. Beside normal metal contacts we also investigate hybrid structures, where the nanowire is contacted by superconducting [6] or a ferromagnetic electrodes. In semiconductor quantum dot structures single electron transport is investigated. By using a dilution refrigerator with a microwave access coherent transitions in the quantum dot will be studied. The latter is essential for the realization of a spin quantum bit in a nanowire quantum dot.          

Contacted InAs nanowires(left) InAs nanowire contacted with four ohmic contacts (right) InAs nanowire quantum dot structures with three gate finger in the center

Selected publications         

[1] M. Indlekofer and Th. Schäpers,
On the Possibility of Using Semiconductor Nanocolumns for the Realization of Quantum Bits,

[2] M. Akabori, K. Sladek, H. Hardtdegen, T. Schäpers, and D. Grützmacher,
Influence of growth temperature on the selective area MOVPE of InAs nanowires on GaAs (111) B using N2 carrier gas
Journal of Crystal Growth, 311, 3813 - 3816 (2009)

[3] Ch. Blömers, Th. Schäpers, T. Richter, R. Calarco, H. Lüth, and M. Marso,
Phase-coherent transport in InN nanowires of various sizes,
Phys. Rev. B 77, 201301 (2008).

[4] Ch. Blömers, Th. Schäpers, T. Richter, R. Calarco, H. Lüth, and M. Marso
Temperature dependence of the phase-coherence length in InN nanowires,
Appl. Phys. Lett. 92, 132101 (2008).

[5] S. Estevez Hernandez, M. Akabori, K. Sladek, Ch. Volk, S. Alagha, H. Hardtdegen, M. G. Pala, N. Demarina, D. Grützmacher, and Th. Schäpers
Spin-orbit coupling and phase coherence in InAs nanowires,
Phys. Rev. B 82, 235303 (2010)

[6] R. Frielinghaus,  I. E. Batov, M. Weides, H. Kohlstedt, R. Calarco, and Th. Schäpers,
Josephson supercurrent in Nb/InN-nanowire/Nb junctions
Appl. Phys. Lett.  96, 132504 (2010).

[7] C. Blömers, M. I. Lepsa, M. Luysberg, D. Gruützmacher, H. Lüth, and Th. Schäpers,
Electronic Phase Coherence in InAs Nanowires
Nano Letters, 11, 3550-3556 (2011) (DOI: 10.1021/nl201102a).

[8] S. Wirths, K. Weis, A. Winden, K. Sladek, C. Volk, S. Alagha, T. E. Weirich, M. von der Ahe, H. Hardtdegen, H. Lüth, N. Demarina, D. Grützmacher, and Th. Schäpers,
Effect of Si-doping on InAs nanowire transport and morphology,
J. Appl. Phys., 110, 053709 (2011) (

[9] R. Frielinghaus, K. Flöhr, K. Sladek, T.E. Weirich, S. Trellenkamp, H. Hardtdegen, Th. Schäpers, C.M. Schneider, C. Meyer, C.
Monitoring structural influences on quantum transport in InAs nanowires
Applied Physics Letters, 101 (2012) 6, 062104

[10] K. Sladek, A. Winden, S. Wirths, K. Weis, Ch. Blömers, Ö. Gül, T. Grap, S. Lenk, M. von der Ahe, T. E. Weirich, H. Hardtdegen, M.I.Lepsa, A. Lysov, Z.A. Li, W. Prost, F.J. Tegude, H. Lüth, Th. Schäpers, D. Grützmacher,
Comparison of InAs nanowire conductivity: influence of growth method and structure
Physica Status Solidi C, 9 (2012) 2, 230 - 234

[11] S. Wirths, M. Mikulics, P. Heintzmann, A. Winden, K. Weis, Ch. Volk, K. Sladek, N. Demarina, H. Hardtdegen, D. Grützmacher, Th. Schäpers,
Preparation of Ohmic contacts to GaAs/AlGaAs-core/shell-nanowires
Applied Physics Letters, 100 (2012) 4, 042103

[12] H. Yao, H.Y. Günel, Ch. Blömers, K. Weis, J. Chi, J.G. Lu, J. Liu, D. Grützmacher, Th. Schäpers,
Phase coherent transport in InSb nanowires
Applied Physics Letters, 101 (2012) 8, 082103

[13] Ch. Blo?mers,J. G. Lu,L. Huang,C. Witte,D. Gru?tzmacher,H. Lu?th,and Th. Scha?pers
Electronic Transport with Dielectric Confinement in Degenerate InN Nanowires
Nano Lett.2012, 12 (2012) 2768?2772

Additional Information


Dr. Mihail Ion Lepsa

Dr. Hilde Hardtdegen

Prof. Dr. Thomas Schäpers


Superconductor-Nanowire Hybrid

Superconductor-Nanowire Hybrids

If a semiconductor nanowire is contacted by two superconducting electron is close proximity a Josephson supercurrent can be observed. More: Superconductor-Nanowire Hybrids …