Spin-splitting in p-type Ge devices

Holmes, S. N.; Newton, Peter; Llandro, J.; Mansell, Rhodri; Barnes, C. H. W.; Morrison, C.; Myronov, Maksym

doi:10.1063/1.4961416

Cited by 10 publications

(9 citation statements)

References 28 publications

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“…In these devices, there is no Rashba-type spin splitting in the two dimensional contact regions as JÁk jj ¼ 0 and DE Rashba $ (J Â k jj )ÁE z % 0, where E z is the electric field in the growth direction and k jj is the linear momentum vector in the plane of the 2DHG contact regions (with components k x and k y ). In the 2DHG, only a Zeeman spin splitting is observed 18 for large D. A cubic (k jj 3 ) dependent Rashba effect has been previously identified [19][20][21] in p-Ge, but this effect is too small to be observed in the wafers measured here due to the low carrier density and large compressive strain. The patterned gates (g1 and g2) control the width of the 1-D channel and the global top gate (g3) controls the carrier density in the channel, see Fig.…”

Section: Cmos (Complementary Metal Oxide Semiconductor)mentioning

confidence: 52%

Quantum ballistic transport in strained epitaxial germanium

Gul

Holmes

Newton

et al. 2017

Applied Physics Letters

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Large scale fabrication using Complementary Metal Oxide Semiconductor compatible technology of semiconductor nanostructures that operate on the principles of quantum transport is an exciting possibility now due to the recent development of ultra-high mobility hole gases in epitaxial germanium grown on standard silicon substrates. We present here a ballistic transport study of patterned surface gates on strained Ge quantum wells with SiGe barriers, which confirms the quantum characteristics of the Ge heavy hole valence band structure in 1-dimension. Quantised conductance at multiples of 2e 2 /h is a universal feature of hole transport in Ge up to 10 Â (2e 2 /h). The behaviour of ballistic plateaus with finite source-drain bias and applied magnetic field is elucidated. In addition, a reordering of the ground state is observed.

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Section: Cmos (Complementary Metal Oxide Semiconductor)mentioning

confidence: 52%

Quantum ballistic transport in strained epitaxial germanium

Gul

Holmes

Newton

et al. 2017

Applied Physics Letters

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“…This large splitting indicates that any mixing of valence-band states is small. The spin splitting in the Shubnikov-de Haas is from the Zeeman effect of the heavy hole, J = 3/2 states and not from any Rashba spin-orbit coupling in the heavyhole band [42]. There is no indication of beating in the Shubnikov-de Haas effect oscillations or multiple fundamental fields.…”

Section: B Transport Measurements At 15 Kmentioning

confidence: 83%

Activated and Metallic Conduction in p -Type Modulation-Doped Ge - Sn Devices

et al. 2020

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Ge 1−x Sn x quantum wells can be incorporated into Si-Ge-based structures with low-carrier effective masses, high mobilities, and the possibility of direct band-gap devices with x ∼ 0.1. However, the electrical properties of p-type Ge 1−x Sn x devices are dominated by a thermally activated mobility and metallic behavior. At 30 mK the transport measurements indicate localization with a mobility of 380 cm 2 /Vs, which is thermally activated with a temperature-independent carrier density of 4 × 10 11 cm −2. This weakly disordered system with conductivity, σ ∼ e 2 /h, where e is the fundamental charge and h is Planck's constant, is a result of negatively charged "Sn-vacancy" complex states in the barrier layers that act as hole traps. A measured hole effective mass of 0.090 ± 0.005m e from the Shubnikov-de Haas effect, where m e is the free electron mass shows that the valence band is heavy hole dominated and is similar to p-type Ge with the compressive strain playing the role of quenching the spin-orbit coupling and shifting the unoccupied lighthole states to higher hole energies. The Ge 1−x Sn x devices have a high quantum mobility of approximately 36 000 cm 2 /Vs that is not thermally activated. The ratio of transport-to-quantum mobility of approximately 0.01 in Ge 1−x Sn x devices is unusual and points to several competing scattering mechanisms in the different experimental regimes.

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“…[1][2][3][4][5][6][7][8][9][10][11] In germanium, the Dyakonov-Perel spin relaxation mechanism is suppressed by the inversion symmetry of the germanium crystal and the influence of the hyperfine interaction is minimal because of the zero nuclear spin of germanium's most abundant isotopes.…”

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confidence: 99%

“…4,15,16 For the realisation of spintronic devices such as the spin-FET, the development of a semiconductor channel with a long spin diffusion length and where spins can be manipulated by the application of an external field, using the Rashba effect for example, is necessary. 17 A thorough comparison of n-type and p-type epilayers is therefore useful to analyse their possible applications in the spintronic and quantum devices.…”

mentioning

confidence: 99%

“…In devices exhibiting parallel conduction, the observation of weak antilocalization has been attributed to the Rashba effect in the quantum well, 15 although the effect is reduced when devices are constructed that do not parallel conduct 3 and the thermal energy should be sufficient to obscure any spin-splitting without much greater doping densities. 4,28 Attributing this Rashba effect to transport through the highly-doped supply layer could explain this discrepancy as well as the unexpected temperature dependence of the phenomenon, where the weak antilocalization appears to vanish at the lowest measurement temperatures.…”

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Weak localization and weak antilocalization in doped germanium epilayers

Newton

Mansell

Holmes

et al. 2017

Applied Physics Letters

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The magnetoresistance of 50 nm thick epilayers of doped germanium is measured at a range of temperatures down to 1.6 K. Both n- and p-type devices show quantum corrections to the conductivity in an applied magnetic field, with n-type devices displaying weak localization and p-type devices showing weak antilocalization. From fits to these data using the Hikami-Larkin-Nagaoka model, the phase coherence length of each device is extracted, as well as the spin diffusion length of the p-type device. We obtain phase coherence lengths as large as 325 nm in the highly doped n-type device, presenting possible applications in quantum technologies. The decay of the phase coherence length with temperature is found to obey the same power law of lϕ ∝ Tc, where c = −0.68 ± 0.03, for each device, in spite of the clear differences in the nature of the conduction. In the p-type device, the measured spin diffusion length does not change over the range of temperatures for which weak antilocalization can be observed. The presence of a spin-orbit interaction manifested as weak antilocalization in the p-type epilayer suggests that these structures could be developed for use in spintronic devices such as the spin-FET, where significant spin lifetimes would be important for efficient device operation.

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Spin-splitting in p-type Ge devices

Cited by 10 publications

References 28 publications

Quantum ballistic transport in strained epitaxial germanium

Quantum ballistic transport in strained epitaxial germanium

Activated and Metallic Conduction in p -Type Modulation-Doped Ge - Sn Devices

Weak localization and weak antilocalization in doped germanium epilayers

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