Ultra-high hole mobility exceeding one million in a strained germanium quantum well

Dobbie, A.; Myronov, Maksym; Morris, R. J. H.; Hassan, A. H. A.; Prest, M. J.; Shah, V. A.; Parker, E. H. C.; Whall, T. E.; Leadley, D. R.

doi:10.1063/1.4763476

Applied Physics Letters

2012

DOI: 10.1063/1.4763476

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Ultra-high hole mobility exceeding one million in a strained germanium quantum well

A. Dobbie¹,

Maksym Myronov²,

R. J. H. Morris³

et al.

Abstract: In this paper, we report a Hall mobility of one million in a germanium two-dimensional hole gas. The extremely high hole mobility of 1.1 × 106 cm2 V−1 s−1 at a carrier sheet density of 3 × 1011 cm−2 was observed at 12 K. This mobility is nearly an order of magnitude higher than any previously reported. From the structural analysis of the material and mobility modeling based on the relaxation time approximation, we attribute this result to the combination of a high purity Ge channel and a very low background im… Show more

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Cited by 86 publications

(75 citation statements)

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“…Strain in a Ge epilayer or QW can be tuned by growth onto a silicon germanium (SiGe) relaxed buffer layer, the magnitude of the strain is tuned through the Ge composition of the buffer. Strain changes the mobility of carriers in Ge, with the highest mobilities to date found in Ge layers grown on an $70-80% Ge SiGe buffer layer [16][17][18]. Ge is highly compatible with conventional Si-based technology, and can be grown with high material and electrical quality onto standard orientation silicon substrates.…”

mentioning

confidence: 99%

“…One of the key advances necessary to observe the Rashba S-O interaction using SdH oscillations is the significant enhancement of 2D hole mobility at low temperatures. Recently, hole mobilities in excess of 1,300,000 cm 2 V À1 s À1 were achieved in strained Ge QW heterostructures [16,[62][63][64], with effective masses as low as 0.035 m 0 [65] comparable to the electron effective mass in certain III-V compound semiconductors and to the light hole mass in bulk Ge. The first observation of the cubic Rashba interaction in a Ge QW utilised a SiGe heterostructure containing a 2DHG in a pure Ge, with a low temperature mobility of 450,000 cm 2 V À1 s À1 [57].…”

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confidence: 99%

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Strained germanium for applications in spintronics

Morrison

Myronov

2016

Physica Status Solidi (a)

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Germanium (Ge) is another group-IV semiconductor material, which recently started attracting tremendous attention in spintronics following success of silicon (Si). The crystal inversion symmetry of Si and Ge precludes the spin relaxation of conduction electrons by the Dyakonov-Perel mechanism, resulting in a long spin relaxation time. Since the proposal of the spin FET in 1990 by Datta and Das, semiconductor materials have been studied for their spin-orbit (S-O) interactions, particularly those that can be modified by an applied electric field, such as the Rashba S-O interaction, in order to create devices that utilise spin modulation and control to perform logic operations. Since then new proposals have appeared. Nowadays they include spin transistors with several different operating principles, spin-based diodes, spin-based field programmable gate arrays, dynamic spin-logic circuits, spin-only logic, spin communication and others. In this review, the focus will be made on presenting recent progress in Ge spintronics including the key advances made. The absence of Dresselhaus S-O coupling in Ge enables a longer spin diffusion length when compared to III-V semiconductor materials. Evidence of a strong Rashba S-O interaction in strained Ge quantum wells has begun to emerge. Also, the first experimental demonstration of room-temperature spin transport in Ge has recently been reported.

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confidence: 99%

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confidence: 99%

Strained germanium for applications in spintronics

Morrison

Myronov

2016

Physica Status Solidi (a)

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“…Thus, the top of the valence band can be tuned to the HH state. Recent advances in Ge and SiGe epitaxial growth technology revealed that it is possible to fabricate a high crystal quality strained-Ge=SiGe QW on Si substrates [23,24]. Thus, strained Ge=SiGe provides a good platform to study the cubic-Rashba SOI in simple single element semiconductors and will offer an interesting comparison with existing SOI theory.…”

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confidence: 99%

Cubic Rashba Spin-Orbit Interaction of a Two-Dimensional Hole Gas in a Strained-Ge/SiGeQuantum Well

et al. 2014

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The spin-orbit interaction (SOI) of a two-dimensional hole gas in the inversion symmetric semiconductor Ge is studied in a strained-Ge=SiGe quantum well structure. We observe weak antilocalization (WAL) in the magnetoconductivity measurement, revealing that the WAL feature can be fully described by the k-cubic Rashba SOI theory. Furthermore, we demonstrate electric field control of the Rashba SOI. Our findings reveal that the heavy hole (HH) in strained Ge is a purely cubic Rashba system, which is consistent with the spin angular momentum m j ¼ AE3=2 nature of the HH wave function. DOI: 10.1103/PhysRevLett.113.086601 PACS numbers: 72.25.Dc, 73.20.Fz, 73.21.-b The spin-orbit interaction (SOI) in a two-dimensional system is a subject of considerable interest because the SOI induces spin splitting at a zero magnetic field, which is important in both fundamental research and electronic device applications [1]. Recent developments of SOI-induced phenomena in the solid state demonstrate many possibilities utilizing spin current and the emergence of new physics such as the spin interferometer [2,3], persistent spin helix [4,5], spin Hall effect [6][7][8], and quantum spin Hall effect [9,10]. Up to now, there have been two well-known SOIs existing in solids: the Dresselhaus SOI [11] due to bulk inversion asymmetry (BIA) in the crystal structure and the Rashba SOI [12,13] due to spatial inversion asymmetry (SIA).In low-dimensional systems, the Rashba SOI becomes more important because it is stronger at the heterointerface and can be controlled by an external electric field. Many of the pioneering studies on the SOI-induced phenomena mentioned above were performed in two-dimensional electron systems, where the Rashba SOI is described by the k-linear Rashba term. In the Hamiltonian, the k-linear Rashba term can be written aswhere σ AE ¼ 1=2ðσ x AE iσ y Þ denote combinations of Pauli spin matrices, k AE ¼ k x AE ik y , and k x , k y are the components of the in-plane wave vector k ∥ . The effective magnetic field Ω 1 ðk ∥ Þ acting on the transport carrier due to the k-linear Rashba term is illustrated in Fig. 1(a).Recently, a higher-order contribution of the Rashba SOI, the so-called k 3 (k-cubic) Rashba SOI, has received more attention [14,15]. The Hamiltonian for the k-cubic Rashba SOI is expressed asand the effective magnetic field Ω 3 ðk ∥ Þ in k space is illustrated in Fig. 1(b) [15]. There is a significant difference in the effective field symmetry between the k-linear and the k-cubic Rashba SOI with one and three rotations in k space, respectively. The k 3 symmetry of the SOI is an interesting subject because it influences all of the SOI-induced phenomena as opposed to the k-linear Rashba term. For example, in case of the spin Hall effect, the k-cubic Rashba term is predicted to give rise to a larger spin Hall conductivity [17][18][19].

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“…Mobility at the lowest temperatures is very high (780 000 cm 2 /Vs), approaching the record value in this class of heterostructures. 1 The carrier density is 2 Â 10 11 cm À2 at 0.3 K, indicating a relatively high transferal of carriers from the doping layer into the QW region.…”

mentioning

confidence: 99%

“…Low temperature 2DHG mobility in excess of 1.3 Â 10 6 cm 2 /Vs has been achieved. 1,[4][5][6] The study of quantum transport behaviour in these 2DHGs at low temperatures, in particular, the Shubnikov de-Haas (SdH) oscillations that arise from Landau levels created under an applied magnetic field, allows us to determine the key parameters such as effective mass, as well as the carrier densities and diffusive and quantum transport scattering parameters.…”

mentioning

confidence: 99%

Complex quantum transport in a modulation doped strained Ge quantum well heterostructure with a high mobility 2D hole gas

Morrison

Casteleiro

Leadley

et al. 2016

Applied Physics Letters

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Ultra-high hole mobility exceeding one million in a strained germanium quantum well

Cited by 86 publications

References 21 publications

Strained germanium for applications in spintronics

Strained germanium for applications in spintronics

Cubic Rashba Spin-Orbit Interaction of a Two-Dimensional Hole Gas in a Strained-Ge/SiGeQuantum Well

Complex quantum transport in a modulation doped strained Ge quantum well heterostructure with a high mobility 2D hole gas

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