(Invited) Low-Temperature Growth of Strained Germanium Quantum Wells for High Mobility Applications

Bedell, Stephen W.; Hart, Sean; Bangsaruntip, Sarunya; Durfee, C. S.; Ott, J. A.; Hopstaken, M; Carroll, Malcolm S.; Gumann, Pat

doi:10.1149/09805.0215ecst

Cited by 3 publications

(5 citation statements)

References 12 publications

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“…The quantum-dot device is fabricated on a Ge/SiGe heterostructure consisting of a 20-nm-thick quantum well buried 48 nm below the wafer surface, grown in an industrial reduced-pressure chemical vapour deposition reactor 26 . The virtual substrate consists of a strain-relaxed germanium layer on a silicon wafer and multiple layers with increasing silicon content to reach the Si 0.2 Ge 0.8 stoichiometry used for the quantum-well barriers.…”

Section: Methodsmentioning

confidence: 99%

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Sweet-spot operation of a germanium hole spin qubit with highly anisotropic noise sensitivity

Hendrickx,

Massai,

Mergenthaler

et al. 2024

Nat. Mater.

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Spin qubits defined by valence band hole states are attractive for quantum information processing due to their inherent coupling to electric fields, enabling fast and scalable qubit control. Heavy holes in germanium are particularly promising, with recent demonstrations of fast and high-fidelity qubit operations. However, the mechanisms and anisotropies that underlie qubit driving and decoherence remain mostly unclear. Here we report the highly anisotropic heavy-hole g-tensor and its dependence on electric fields, revealing how qubit driving and decoherence originate from electric modulations of the g-tensor. Furthermore, we confirm the predicted Ising-type hyperfine interaction and show that qubit coherence is ultimately limited by 1/f charge noise, where f is the frequency. Finally, operating the qubit at low magnetic field, we measure a dephasing time of $${T}_{2}^{* }$$ T 2 * = 17.6 μs, maintaining single-qubit gate fidelities well above 99% even at elevated temperatures of T > 1 K. This understanding of qubit driving and decoherence mechanisms is key towards realizing scalable and highly coherent hole qubit arrays.

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Section: Methodsmentioning

confidence: 99%

“…We define a two-qubit system based on confined hole spins in a strained Ge/SiGe heterostructure quantum well 26 . The spins are confined in gate-defined quantum dots, formed respectively underneath plunger gates P1 and P2, with an additional gate B12 controlling the interdot coupling (Fig.…”

Section: Germanium Two-qubit Devicementioning

confidence: 99%

Sweet-spot operation of a germanium hole spin qubit with highly anisotropic noise sensitivity

Hendrickx,

Massai,

Mergenthaler

et al. 2024

Nat. Mater.

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“…The use of a low temperature for the re-epitaxy of the 2DHG heterostructure (500°C here compared to, for instance, 500°C in Ref. (23) or 550°C in Ref. ( 29)) might indeed have led to deleterious O contamination (12).…”

Section: (Right))mentioning

confidence: 98%

“…RLGs yielded record breaking hole mobility in a 2DHG inside a compressively strained Ge QW embedded in SiGe 80% (21). Similar approaches are currently being used, without boron-doped supply layers, however, by TU Delft (22) and IBM Yorktown (23) to fabricate hole spin qubits ( 6), (24).…”

Section: Sige Virtual Substrate Growthmentioning

confidence: 99%

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Epitaxy of Group-IV Semiconductors for Quantum Electronics

Hartmann,

Bernier,

Pierre

et al. 2023

ECS Trans.

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We are growing at CEA (i) high purity 28Si layers and (ii) c-Ge/SiGe heterostructures for electron and hole spin quantum bits. We describe here strategies usable for the fabrication of 28SOI substrates, with a focus on 28SiH4 consumption minimization, as such a gas is very expensive and hard to come by. We also focus on the properties of Si0.26Ge0.74 and Si0.21Ge0.79 Virtual Substrates (VS) grown at 850°C, 20 Torr and a forward Ge ramping-up on Si(001) substrates. After some chemical polishing (to remove the surface cross-hatch), those VS are used as templates for the 500°C, 100 Torr growth of SiGe/c-Ge/SiGe 2D Hole Gas Gas (2DHG) stacks. Those c-Ge layers are, in X-Ray Diffraction, fully compressively strained on the relaxed SiGe VS underneath and of high crystalline quality. Some slight undulations are evidenced at c-Ge / SiGe cap interfaces, hinting at elastic strain relaxation, however. Magnetotransport measurements in Hall-bar devices were performed at 4.2 K to assess the electrical properties of the 2DHG in those SiGe/c-Ge heterostructures. At low magnetic field, a hole mobility of 1.2 x 105 cm2 V-1 s-1 was obtained for a hole density of n2DHG = 3.7x1011 cm-2 in a 16 nm thick c-Ge/55 nm thick Si0.21Ge0.79 cap sample.

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Impact of interface traps on charge noise and low-density transport properties in Ge/SiGe heterostructures

Massai,

Hetényi,

Mergenthaler

et al. 2024

Commun Mater

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Hole spins in Ge/SiGe heterostructures have emerged as an interesting qubit platform with favourable properties such as fast electrical control and noise-resilient operation at sweet spots. However, commonly observed gate-induced electrostatic disorder, drifts, and hysteresis hinder reproducible tune-up of SiGe-based quantum dot arrays. Here, we study Hall bar and quantum dot devices fabricated on Ge/SiGe heterostructures and present a consistent model for the origin of gate hysteresis and its impact on transport metrics and charge noise. As we push the accumulation voltages more negative, we observe non-monotonous changes in the low-density transport metrics, attributed to the induced gradual filling of a spatially varying density of charge traps at the SiGe-oxide interface. With each gate voltage push, we find local activation of a transient low-frequency charge noise component that completely vanishes again after 30 hours. Our results highlight the resilience of the SiGe material platform to interface-trap-induced disorder and noise and pave the way for reproducible tuning of larger multi-dot systems.

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(Invited) Low-Temperature Growth of Strained Germanium Quantum Wells for High Mobility Applications

Cited by 3 publications

References 12 publications

Sweet-spot operation of a germanium hole spin qubit with highly anisotropic noise sensitivity

Sweet-spot operation of a germanium hole spin qubit with highly anisotropic noise sensitivity

Epitaxy of Group-IV Semiconductors for Quantum Electronics

Impact of interface traps on charge noise and low-density transport properties in Ge/SiGe heterostructures

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