Elastically relaxed free-standing strained-silicon nanomembranes

Roberts, Michelle; Klein, Levente J.; Savage, D. E.; Slinker, Keith; Friesen, Mark; Celler, G. K.; Eriksson, M. A.; Lagally, M. G.

doi:10.1038/nmat1606

Cited by 245 publications

(254 citation statements)

References 26 publications

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“…1 In existing demonstrations of this effect in covalent semiconductors, such as Si, the elastic compliance of nanoscale sheets can be used to create heterostructures that enable new strategies for the realization of quantum devices without defects resulting from plastic relaxation. 2,3 A persistent challenge in advancing towards thin materials in perovskite complex oxides, however, is that lithographic processing of thin substrates can lead to low structural quality in terms of non-uniform thickness, roughness, buckling, or defect density. [4][5][6] Alternative approaches based on chemical exfoliation of large-unit-cell oxide compounds can create ultrathin substrates but have a severely limited range of compositions and crystallographic orientations.…”

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confidence: 99%

Fabrication and convergent X-ray nanobeam diffraction characterization of submicron-thickness SrTiO3 crystalline sheets

et al. 2016

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The creation of thin SrTiO3 crystals from (001)-oriented SrTiO3 bulk single crystals using focused ion beam milling techniques yields sheets with submicron thickness and arbitrary orientation within the (001) plane. Synchrotron x-ray nanodiffraction rocking curve widths of these SrTiO3 sheets are less than 0.02°, less than a factor of two larger than bulk SrTiO3, making these crystals suitable substrates for epitaxial thin film growth. The change in the rocking curve width is sufficiently small that we deduce that dislocations are not introduced into the SrTiO3 sheets. Observed lattice distortions are consistent with a low concentration of point defects.

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Fabrication and convergent X-ray nanobeam diffraction characterization of submicron-thickness SrTiO3 crystalline sheets

et al. 2016

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“…We utilize a fabrication process that is fully compatible with mainstream complementary metal oxide semiconductor (CMOS) technology. Our bridges are fabricated from SSOI substrates, but the concept can be generalized and used for any tensile strained layer, including free standing defect free Si/SiGe heterostructure membranes 13 . We show that the strain can be controlled accurately by designing the dimensions of the bridge, producing a uniform longitudinal strain in the NW.…”

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Top-down fabricated silicon nanowires under tensile elastic strain up to 4.5%

et al. 2012

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strained si nanowires are among the most promising transistor structures for implementation in very large-scale integration due to of their superior electrostatic control and enhanced transport properties. Realizing even higher strain levels within such nanowires are thus one of the current challenges in microelectronics. Here we achieve 4.5% of elastic strain (7.6 GPa uniaxial tensile stress) in 30 nm wide si nanowires, which considerably exceeds the limit that can be obtained using siGe-based virtual substrates. our approach is based on strain accumulation mechanisms in suspended dumbbell-shaped bridges patterned on strained si-on-insulator, and is compatible with complementary metal oxide semiconductor fabrication. Potentially, this method can be applied to any tensile prestrained layer, provided the layer can be released from the substrate, enabling the fabrication of a variety of strained semiconductors with unique properties for applications in nanoelectronics, photonics and photovoltaics. This method also opens up opportunities for research on strained materials.

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“…An alternative approach is to develop heterostructures utilizing strain-sharing techniques, 22 which can, in principle, provide step-free interfaces. Indeed, large valley splittings have be obtained in similar unstrained silicon oxide structures.…”

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Magnetic field dependence of valley splitting in realistic Si∕SiGe quantum wells

Friesen¹,

Eriksson²,

Coppersmith³

2006

Applied Physics Letters

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115

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The authors investigate the magnetic field dependence of the energy splitting between low-lying valley states for electrons in a Si/SiGe quantum well tilted with respect to the crystallographic axis. The presence of atomic steps at the quantum well interface may explain the unexpected, strong suppression of the valley splitting observed in recent experiments. The authors find that the suppression is caused by an interference effect associated with multiple steps, and that the magnetic field dependence arises from the lateral confinement of the electronic wave function. Using numerical simulations, the authors clarify the role of step disorder, obtaining quantitative agreement with the experiments.Qubits in silicon are leading candidates for scalable quantum computing, owing to their favorable and well studied materials properties.1,2 Indeed, because of its prominence in the electronics industry, silicon may be the best understood semiconducting material. However, as devices continue to shrink in size, approaching the quantum regime, important questions arise. Unlike direct gap semiconductors, the conduction band structure in silicon possesses six symmetric minima or "valleys" that are not at the Brillouin zone center. Consequently, the minima are degenerate, and must be described by a valley index which competes with the spin index as a relevant quantum number in the qubit Hilbert space.3 Therefore, to construct spin qubits in silicon, it is necessary to lift all valley degeneracy.A silicon quantum well grown on the [001] surface of strain-relaxed silicon-germanium is under tensile strain, causing the four lateral valleys to rise significantly in energy.4 At low temperatures, only the two low-lying valleys are populated. The remaining two-fold degeneracy can be removed by the sharp confinement potential of the quantum well interface.5 Theoretical estimates suggest that the resulting valley splitting can be of the order of 1 meV ≈ 12 K, 6 which is sufficiently large for quantum computing. However, recent experiments in SiGe 7,8,9,10 measure a valley splitting much smaller than the theoretical prediction. There is currently no explanation for this discrepency.11 Indeed, a prevalent theory 12 predicts an enhancement of the valley splitting in a magnetic field that is different from the experimental observations.In this letter, we describe a single-electron valley splitting theory for silicon quantum wells grown on a vicinal substrate, building upon an initial suggestion by Ando. 13Such miscuts are often incorporated into Si/SiGe heterostructures to ensure uniform growth surfaces and to avoid step bunching. The resulting quantum well, obtained by conformal epitaxial deposition, is misaligned with respect to the crystallographic z axis, as shown in Fig. 1. We now describe the effective mass theory and explain how the presence of interfacial atomic steps suppresses valley splitting.For silicon strained in the [001] direction, the effective mass wavefunction 14 can be written as a sum of contributions from the two z va...

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Elastically relaxed free-standing strained-silicon nanomembranes

Cited by 245 publications

References 26 publications

Fabrication and convergent X-ray nanobeam diffraction characterization of submicron-thickness SrTiO3 crystalline sheets

Fabrication and convergent X-ray nanobeam diffraction characterization of submicron-thickness SrTiO3 crystalline sheets

Top-down fabricated silicon nanowires under tensile elastic strain up to 4.5%

Magnetic field dependence of valley splitting in realistic Si∕SiGe quantum wells

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