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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. Blömers,J. G. Lu,L. Huang,C. Witte,D. Grützmacher,H. Lüth,and Th. Schäpers
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 …