Magneto-transport analysis of an ultra-low-density two-dimensional hole gas in an undoped strained Ge/SiGe heterostructure

Laroche, Dominique; Huang, S.-H.; Chuang, Yen; Li, J.-Y.; C, Liu; Lu, Tzu-Ming

doi:10.1063/1.4953399

Cited by 25 publications

(33 citation statements)

References 42 publications

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“…By fitting the data to a power law dependence

μ = p_{2 D}^{α}

, we find a large exponent α = 2.1. Including local field corrections, exponents α ≥ 1.5 indicate that the mobility is still limited by scattering from remote impurities at the dielectric/semiconductor interface, as seen previously in Si/SiGe heterostructures . At saturation density p 2D = 6 × 10 11 cm −2 we measure a maximum mobility of 5 × 10 5 cm 2 V −1 s −1 , corresponding to a mean free path of ≈6 µm, setting new benchmarks for holes in shallow H‐FET devices.…”

Section: Resultssupporting

confidence: 60%

“…Indeed, gate controlled quantum dots, ballistic 1D channels, and ballistic phase coherent superconductivity were demonstrated recently by using undoped Ge/SiGe. So far the added complexity in developing reliable gate‐stacks has limited the investigation of quantum transport properties in undoped Ge/SiGe to devices with mobilities significantly inferior compared to modulation‐doped structures …”

Section: Introductionmentioning

confidence: 99%

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Shallow and Undoped Germanium Quantum Wells: A Playground for Spin and Hybrid Quantum Technology

Sammak

Sabbagh

Hendrickx

et al. 2019

Adv Funct Materials

112

126

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Buried-channel semiconductor heterostructures are an archetype material platform for the fabrication of gated semiconductor quantum devices. Sharp confinement potential is obtained by positioning the channel near the surface; however, nearby surface states degrade the electrical properties of the starting material. Here, a 2D hole gas of high mobility (5 × 10 5 cm 2 V −1 s −1 ) is demonstrated in a very shallow strained germanium (Ge) channel, which is located only 22 nm below the surface. The top-gate of a dopant-less field effect transistor controls the channel carrier density confined in an undoped Ge/SiGe heterostructure with reduced background contamination, sharp interfaces, and high uniformity. The high mobility leads to mean free paths ≈ 6 µm, setting new benchmarks for holes in shallow field effect transistors. The high mobility, along with a percolation density of 1.2 × 10 11 cm −2 , light effective mass (0.09m e ), and high effective g-factor (up to 9.2) highlight the potential of undoped Ge/SiGe as a low-disorder material platform for hybrid quantum technologies.

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“…By fitting the data to a power law dependence

μ = p_{2 D}^{α}

Section: Resultssupporting

confidence: 60%

Section: Introductionmentioning

confidence: 99%

Shallow and Undoped Germanium Quantum Wells: A Playground for Spin and Hybrid Quantum Technology

Sammak

Sabbagh

Hendrickx

et al. 2019

Adv Funct Materials

112

126

View full text Add to dashboard Cite

show abstract

“…33 We first performed transport characterization of Hall bars (see the Supporting Information and Ref. 34 ), the results of which attest to the high quality of the material and suggest that it is favorable for hosting hole quantum dots. The effective mass of holes in this system is found to be m* ~0.08 m0 (where m0 is the bare electron mass), close to that of electrons in GaAs (m* ~0.067 m 0 ).…”

Section: Resultsmentioning

confidence: 99%

Single and double hole quantum dots in strained Ge/SiGe quantum wells

Hardy

Harris

et al. 2019

Nanotechnology

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Even as today's most prominent spin-based qubit technologies are maturing in terms of capability and sophistication, there is growing interest in exploring alternate material platforms that may provide advantages, such as enhanced qubit control, longer coherence times, and improved extensibility. Recent advances in heterostructure material growth have opened new possibilities for employing hole spins in semiconductors for qubit applications. Undoped, strained Ge/SiGe quantum wells are promising candidate hosts for hole spin-based qubits due to their low disorder, large intrinsic spin-orbit coupling strength, and absence of valley states. Here, we use a simple one-layer gated device structure to demonstrate both a single quantum dot as well as coupling 2 between two adjacent quantum dots. The hole effective mass in these undoped structures, m* ~ 0.08 m0, is significantly lower than for electrons in Si/SiGe, pointing to the possibility of enhanced tunnel couplings in quantum dots and favorable qubit-qubit interactions in an industry-compatible semiconductor platform. CONCLUSIONSWe have demonstrated lithographically defined single and double hole quantum dots in high quality strained Ge/SiGe quantum wells. These results strongly suggest that this material system may serve as a viable host for spin-based qubits (compatible with CMOS processing) and enable quantitative comparisons between quantum dots in electron and hole systems. Multi-metal-layer devices, as are commonly used in Si/SiGe, should be directly applicable to Ge/SiGe to increase the sharpness of tunnel barriers and provide more orthogonal control of coupling between adjacent quantum dots. Development of successful qubit architectures will ultimately call for indepth studies of qubit decoherence mechanisms in this system, in particular the impact of charge noise due to the enhanced spin-orbit coupling. AUTHOR INFORMATION

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“…In Ref. [21] a rather large effective mass of 0.105m e was reported at a low density of 1 × 10 11 cm −2 . Furthermore, no clear dependence of the effective mass with density could be extracted in the investigated arXiv:1905.08064v1 [cond-mat.mes-hall] 20 May 2019 range from ∼ 0.6 × 10 11 cm −2 to ∼ 1.4 × 10 11 cm −2 .…”

mentioning

confidence: 94%

Light effective hole mass in undoped Ge/SiGe quantum wells

et al. 2019

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We report density-dependent effective hole mass measurements in undoped germanium quantum wells. We are able to span a large range of densities (2.0 − 11 × 10 11 cm −2 ) in top-gated field effect transistors by positioning the strained buried Ge channel at different depths of 12 and 44 nm from the surface. From the thermal damping of the amplitude of Shubnikov-de Haas oscillations, we measure a light mass of 0.061me at a density of 2.2 × 10 11 cm −2 . We confirm the theoretically predicted dependence of increasing mass with density and by extrapolation we find an effective mass of ∼ 0.05me at zero density, the lightest effective mass for a planar platform that demonstrated spin qubits in quantum dots.Holes are rapidly emerging as a promising candidate for semiconductor quantum computing.[1-3] In particular, holes in germanium (Ge) bear favorable properties for quantum operation, such as strong spin-orbit coupling enabling electric driving without the need of microscopic objects,[1-3] large excited state splitting energies to isolate the qubit states, [4] and ohmic contacts to virtually all metals for hybrid superconducting-semiconducting research [5][6][7][8][9]. Furthermore, undoped planar Ge quantum wells with hole mobilities µ > 5 × 10 5 cm 2 /Vs were recently developed[10] and shown to support quantum dots [11,12] and single and two qubit logic,[3] providing scope to scale up the number of qubits.

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Magneto-transport analysis of an ultra-low-density two-dimensional hole gas in an undoped strained Ge/SiGe heterostructure

Cited by 25 publications

References 42 publications

Shallow and Undoped Germanium Quantum Wells: A Playground for Spin and Hybrid Quantum Technology

Shallow and Undoped Germanium Quantum Wells: A Playground for Spin and Hybrid Quantum Technology

Single and double hole quantum dots in strained Ge/SiGe quantum wells

Light effective hole mass in undoped Ge/SiGe quantum wells

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