One-Dimensional Hole Gas in Germanium/Silicon Nanowire Heterostructures

Abstract

Two-dimensional electron and hole gas systems, enabled through band structure design and epitaxial growth on planar substrates, have served as key platforms for fundamental condensed matter research and high performance devices. The analogous development of one-dimensional (1D) electron or hole gas systems through controlled growth on 1D nanostructure substrates, which could open up opportunities beyond existing carbon nanotube and nanowire systems, has not been realized. Here we report the synthesis and transport studies of a 1D hole gas system based on a free-standing germanium/silicon (Ge/Si) core/shell nanowire heterostructure. Room temperature electrical transport measurements show clearly hole accumulation in undoped Ge/Si nanowire heterostructures, in contrast to control experiments on single component nanowires. Low-temperature studies show well controlled Coulomb blockade oscillations when the Si shell serves as a tunnel barrier to the hole gas in the Ge channel. Transparent contacts to the hole gas also have been reproducibly achieved by thermal annealing. In such devices, we observe conductance quantization at low temperatures, corresponding to ballistic transport through 1D subbands, where the measured subband energy spacings agree with calculations for a cylindrical confinement potential. In addition, we observe a 0.7 structure, which has been attributed to spontaneous spin polarization, suggesting the universality of this phenomenon in interacting 1D systems. Lastly, the conductance exhibits little temperature dependence, consistent with our calculation of reduced backscattering in this 1D system, and suggests that transport is ballistic even at room temperature.

17 pages, 5 figures

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• Luttinger Liquid Behavior in Carbon Nanotubes
• Possible Spin Polarization in a One-Dimensional Electron Gas
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• Disorder, pseudospins, and backscattering in carbon nanotubes
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• Bias and temperature dependence of the 0.7 conductance anomaly in Quantum Point Contacts
• Coherent Single Charge Transport in Molecular-Scale Silicon Nanowire Transistors
• Density dependent spin polarisation in ultra low-disorder quantum wires
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• Gate-controlled quantum dots and superconductivity in planar germanium
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• Large scale and linear scaling DFT with the CONQUEST code
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• Ballistic quantum transport through Ge/Si core/shell nanowires
• HADOKEN: An Open-Source Software Package for Predicting Electron Confinement Effects in Various Nanowire Geometries and Configurations
• Efficient Chebyshev polynomial approach to quantum conductance calculations: Application to twisted bilayer graphene
• Scaling Properties of Ge-SixGe1-x Core-Shell Nanowire Field Effect Transistors
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• Scalable and Tunable In-Plane Ge/Si(001) Nanowires Grown by Molecular Beam Epitaxy
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