One-dimensional hole gas in germanium/silicon nanowire heterostructures

One-dimensional hole gas in germanium/silicon nanowire heterostructures,10.1073/pnas.0504581102,Proceedings of The National Academy of Sciences,Wei Lu

One-dimensional hole gas in germanium/silicon nanowire heterostructures   (Citations: 39)
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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 clearly show 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. Author contributions: W.L., J.X., and C.M.L. designed research; W.L. and J.X. performed research; B.P.T. and Y.W. contributed new reagents/analytic tools; W.L., J.X., and C.M.L. analyzed data; W.L., J.X., and C.M.L. wrote the paper; and B.P.T. and Y.W. developed growth of nanowire heterostructure.Freely available online through the PNAS open access option.Abbreviations: i-Ge, intrinsic Ge; i-Si, intrinsic Si; sccm, standard cm3/min.‡W.L. and J.X. contributed equally to this work.
Journal: Proceedings of The National Academy of Sciences - PNAS , vol. 1021, no. 29, pp. 10046-10051, 2005
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