Ultrasmall silicon quantum dots

Zwanenburg, Floris A.; Loon, A. A. van; Steele, Gary A.; Rijmenam, Cathalijn E. W. M. van; Balder, T.; Fang, Ying; Lieber, Charles M.; Kouwenhoven, Leo P.

doi:10.1063/1.3155854

Cited by 22 publications

(29 citation statements)

References 22 publications

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“…19 Further, this architecture due to the strong spin-orbit coupling of holes in Ge could be an attractive candidate for the study of Majorana zero modes and development of topological superconducting qubits. 16,20 Our approach for the synthesis of a monolithic Al-Ge/Si-Al NW heterostructure featuring highly transparent contacts to a 1D hole gas is based on vapor-liquid-solid 21 to the converted c-Al region the intensity changes over about 1 nm. However, if we measure the local lattice spacing, as shown in the inset, we find the last plane of higher HAADF STEM intensity has the lattice spacing close to the value of a Ge (111) plane (about 0.32 nm).…”

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confidence: 99%

“…These observations clearly demonstrate that such a device, with a short channel, possess gate voltage mediated superconducting proximity effect. 32,33 As the Ge/Si 20 or Ge/Si core/shell based NW devices contacting the Si-shell, 35 forming a tunnel barrier at low temperatures. These findings further indicate that our Al-Ge/Si-Al heterostructure devices feature highly transparent contacts to the 1D hole gas, which is in good agreement with Xiang et al 8 In the low conducting regime (25 V < VG < 30 V) we observe a superconducting gap with a minimum gap ratio of <GG> / <GN> = 0.03, where <GG> is the average conductance inside the gap, across a VD range from -0.05 mV to 0.05 mV, and <GN> the average conductance outside the gap, across a VD range from -0.7 mV to -0.6 mV.…”

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confidence: 99%

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Highly Transparent Contacts to the 1D Hole Gas in Ultrascaled Ge/Si Core/Shell Nanowires

et al. 2019

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Semiconductor-superconductor hybrid systems have outstanding potential for emerging high performance nanoelectronics and quantum devices. However, critical to their successful application is the fabrication of high quality and reproducible semiconductor-superconductor interfaces. Here, we realize and measure axial Al-Ge-Al nanowire heterostructures with atomically precise interfaces, enwrapped by an ultra-thin epitaxial Si layer further denoted as Al-Ge/Si-Al nanowire heterostructures. The heterostructures were synthesized by a thermally induced exchange reaction of single-crystalline Ge/Si core/shell nanowires and lithographically defined Al contact pads. Applying this heterostructure formation scheme enables self-aligned quasi one-dimensional crystalline Al leads contacting ultra-scaled Ge/Si segments with contact transparencies greater than 98%. Integration into back-gated field-effect devices and continuous scaling beyond lithographic limitations allows us to exploit the full potential of the highly transparent contacts to the 1D hole gas at the Ge-Si interface. This leads to the observation of ballistic transport as well as quantum confinement effects up to temperatures of 150 K. Low temperature measurements reveal proximity-induced superconductivity in the Ge/Si core/shell nanowires. The realization of a Josephson field-effect transistor allows us to study the subharmonic energy-gap structure caused by multiple Andreev reflections. Most importantly, the absence of a quantum dot regime indicates a hard superconducting gap originating from the highly transparent contacts to the 1D hole-gas,

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confidence: 99%

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confidence: 99%

Highly Transparent Contacts to the 1D Hole Gas in Ultrascaled Ge/Si Core/Shell Nanowires

et al. 2019

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“…Although the quantum dot technology is not yet as mature as in GaAs, several perspective setups are being actively pursued. [20][21][22][23][24][25][26] In addition to the absence of nuclear spins, Si seems potentially advantageous because of weaker spin-orbit interactions, promising less decoherence, and a stronger g-factor, allowing spin control at smaller magnetic fields.…”

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confidence: 99%

Theory of single electron spin relaxation in Si/SiGe lateral coupled quantum dots

2011

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We investigate the spin relaxation induced by acoustic phonons in the presence of spin-orbit interactions in single electron Si/SiGe lateral coupled quantum dots. The relaxation rates are computed numerically in single and double quantum dots, in in-plane and perpendicular magnetic fields. The deformation potential of acoustic phonons is taken into account for both transverse and longitudinal polarizations and their contributions to the total relaxation rate are discussed with respect to the dilatation and shear potential constants. We find that in single dots the spin relaxation rate scales approximately with the seventh power of the magnetic field, in line with a recent experiment. In double dots the relaxation rate is much more sensitive to the dot spectrum structure, as it is often dominated by a spin hot spot. The anisotropy of the spin-orbit interactions gives rise to easy passages, special directions of the magnetic field for which the relaxation is strongly suppressed. Quantitatively, the spin relaxation rates in Si are typically 2 orders of magnitude smaller than in GaAs due to the absence of the piezoelectric phonon potential and generally weaker spinorbit interactions.

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“…19 However, suspended p-type single hole transistors have not been investigated previously and even for the case of non-suspended devices, [20][21][22] there are relatively few investigations compared with n-type SETs. 23,24 Single-hole transistors extend the single-electron and QD family of devices to include complementary n-and p-type devices, greatly enhancing flexibility in the design of few-electron, nanoelectronic systems.…”

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Resonant tunnelling features in a suspended silicon nanowire single-hole transistor

Llobet

Krali

Wang

et al. 2015

Applied Physics Letters

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Suspended silicon nanowires have significant potential for a broad spectrum of device applications. A suspended p-type Si nanowire incorporating Si nanocrystal quantum dots has been used to form a single-hole transistor. Transistor fabrication uses a novel and rapid process, based on focused gallium ion beam exposure and anisotropic wet etching, generating <10 nm nanocrystals inside suspended Si nanowires. Electrical characteristics at 10 K show Coulomb diamonds with charging energy ∼27 meV, associated with a single dominant nanocrystal. Resonant tunnelling features with energy spacing ∼10 meV are observed, parallel to both diamond edges. These may be associated either with excited states or hole–acoustic phonon interactions, in the nanocrystal. In the latter case, the energy spacing corresponds well with reported Raman spectroscopy results and phonon spectra calculations.

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Ultrasmall silicon quantum dots

Cited by 22 publications

References 22 publications

Highly Transparent Contacts to the 1D Hole Gas in Ultrascaled Ge/Si Core/Shell Nanowires

Highly Transparent Contacts to the 1D Hole Gas in Ultrascaled Ge/Si Core/Shell Nanowires

Theory of single electron spin relaxation in Si/SiGe lateral coupled quantum dots

Resonant tunnelling features in a suspended silicon nanowire single-hole transistor

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