Role of Confinement on Carrier Transport in Ge–SixGe1–x Core–Shell Nanowires

Nah, Junghyo; Dillen, David C.; Varahramyan, K.; Banerjee, Sanjay K.; Tutuc, Emanuel

doi:10.1021/nl2030695

Cited by 37 publications

(56 citation statements)

References 32 publications

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“…Ge nanowires (NWs) receive growing attention because their integration in electronic devices could present several advantages. [1][2][3][4][5][6][7][8][9] NWs in general are promising channels for ultimate transistors, thanks to excellent gate control and reduced short channel effects. 10 They are also attractive building blocks for flexible electronics.…”

Section: Carrier Mobility In Strained Ge Nanowiresmentioning

confidence: 99%

Carrier mobility in strained Ge nanowires

Niquet

Delerue

2012

Journal of Applied Physics

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We present fully atomistic calculations of the electron and hole mobilities in Ge nanowires with diameter up to 10 nm. We show that the phonon-limited mobility is strongly dependent on the diameter and on the orientation of the nanowire, and is also very responsive to unaxial strains. The similarities and differences with the case of Si nanowires are highlighted. In strained Ge nanowires, the mobility can reach >3000 cm2/V/s for electrons and 12000 cm2/V/s for holes. Ge nanowires are therefore promising nanostructures for ultimate electronic devices.

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Section: Carrier Mobility In Strained Ge Nanowiresmentioning

confidence: 99%

Carrier mobility in strained Ge nanowires

Niquet

Delerue

2012

Journal of Applied Physics

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“…The p-type symmetry of the hole Bloch states gives rise to a total angular momentum J = 3/2, which results in an unusually large, and electrically tunable Rashba-type SOI [34]. Furthermore, the holes show high mobilities [38,42], long mean free paths [37], and Coulomb interaction strongly influences their properties [45]. Longitudinal confinement in these NWs results in tunable single and double QDs [40] with anisotropic and confinement-dependent g factors [46,47], in long relaxation [43] and coherence times [48] as well as in short SOI lengths [49].…”

Section: Introductionmentioning

confidence: 99%

Majorana fermions in Ge/Si hole nanowires

2014

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We consider Ge/Si core/shell nanowires with hole states coupled to an s-wave superconductor in the presence of electric and magnetic fields. We employ a microscopic model that takes into account material-specific details of the band structure such as strong and electrically tunable Rashba-type spin-orbit interaction and g factor anisotropy for the holes. In addition, the proximity-induced superconductivity Hamiltonian is derived starting from a microscopic model. In the topological phase, the nanowires host Majorana fermions with localization lengths that depend strongly on both the magnetic and electric fields. We identify the optimal regime in terms of the directions and magnitudes of the fields in which the Majorana fermions are the most localized at the nanowire ends. In short nanowires, the Majorana fermions hybridize and form a subgap fermion whose energy is split away from zero and oscillates as a function of the applied fields. The period of these oscillations could be used to measure the dependence of the spin-orbit interaction on the applied electric field and the g factor anisotropy.

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“…5,9 The latter may therefore be substantially prolonged in group-IV NWs that can be grown nuclearspin-free. In this context, Ge and Si have emerged as promising materials for nanoscale systems such as lateral QDs, [23][24][25][26] self-assembled QDs, [27][28][29] cylindrical core/shell NWs, [10][11][12][13][14][15][16][17][18][19][20] and ultrathin, triangular NWs. 21 For applications in spintronics and quantum information processing, it can be advantageous to consider holes instead of electrons.…”

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confidence: 99%

Tunablegfactor and phonon-mediated hole spin relaxation in Ge/Si nanowire quantum dots

2013

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We theoretically consider g factor and spin lifetimes of holes in a longitudinal Ge/Si core/shell nanowire quantum dot that is exposed to external magnetic and electric fields. For the ground states, we find a large anisotropy of the g factor which is highly tunable by applying electric fields. This tunability depends strongly on the direction of the electric field with respect to the magnetic field. We calculate the single-phonon hole spin relaxation times T1 for zero and small electric fields and propose an optimal setup in which very large T1 of the order of tens of milliseconds can be reached. Increasing the relative shell thickness or the longitudinal confinement length further prolongs T1. In the absence of electric fields, the dephasing vanishes and the decoherence time T2 is determined by T2 = 2T1.PACS numbers: 71.70. Ej, 81.07.Vb, 81.07.Ta Semiconducting nanowires (NWs) allow to create nanoscale systems defined precisely regarding composition, geometry, and electronic properties and hence are subject to great experimental efforts. Furthermore, they offer new ways for implementing spin-based quantum computation.1 Both III-V compounds and group-IV materials are considered and operated in the conduction band (CB, electrons) 2-9 and in the valence band (VB, holes)10-22 regime. A particularly favored material is InAs, where single-electron quantum dots (QDs) 3 and electrically controlled spin rotations 5,6,8 have been implemented. Recently, qubits have also been implemented in InSb NW QDs, 7,9,22 a system for which extremely large electron g factors have been found. 4,7 However, the strong hyperfine interaction in InAs and InSb is considered the dominant source for the short coherence times observed.5,9 The latter may therefore be substantially prolonged in group-IV NWs that can be grown nuclearspin-free. In this context, Ge and Si have emerged as promising materials for nanoscale systems such as lateral QDs, 23-26 self-assembled QDs, 27-29 cylindrical core/shell NWs, 10-20 and ultrathin, triangular NWs. 21For applications in spintronics and quantum information processing, it can be advantageous to consider holes instead of electrons. Due to the p-wave symmetry of the Bloch states, holes experience a strong spin-orbit interaction (SOI) on the atomic level leading to an effective spin J = 3/2 behavior. Hence spin and momentum are coupled strongly which allows efficient control of the hole spin by electrical means. Furthermore, hole spin lifetimes are prolonged in the presence of confinement. 30-35In Ge/Si core/shell NWs, the large VB offset leads to an accumulation of holes in the core.11,36 They form a one dimensional (1D) hole gas with an unusually large, tunable Rashba-type SOI, referred to as direct Rashba SOI (DRSOI).37 This DRSOI makes Ge/Si core/shell NWs attractive candidates for quantum information processing via electric-dipole induced spin resonance, 38 and we mention that signatures of a tunable Rashba SOI were already deduced from magnetotransport experiments. 17Experiments on gate defined QDs...

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Role of Confinement on Carrier Transport in Ge–Si_xGe_1–x Core–Shell Nanowires

Cited by 37 publications

References 32 publications

Carrier mobility in strained Ge nanowires

Carrier mobility in strained Ge nanowires

Majorana fermions in Ge/Si hole nanowires

Tunablegfactor and phonon-mediated hole spin relaxation in Ge/Si nanowire quantum dots

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