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

Nanotechnology

Hardy, Will H.; Harris, C.T.; Su, Yi H.; Chuang, Yen; Moussa, Jonathan; Maurer, Leon M.; Li, Jiun Y.; Lu, Tzu-Ming L.; Luhman, Dwight R.

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 between two adjacent quantum dots. The hole effective mass in these undoped structures, m∗ ∼ 0.08 m 0, 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.

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TYPE Journal Article YEAR 2019
ScopusOSTIDOI

Gate-defined quantum dots in Ge/SiGe quantum wells as a platform for spin qubits

ECS Transactions

Hardy, Will H.; Su, Y.H.; Chuang, Y.; Maurer, L.N.; Brickson, M.; Baczewski, Andrew D.; Li, J.Y.; Lu, Tzu-Ming L.; Luhman, Dwight R.

In the field of semiconductor quantum dot spin qubits, there is growing interest in leveraging the unique properties of hole-carrier systems and their intrinsically strong spin-orbit coupling to engineer novel qubits. Recent advances in semiconductor heterostructure growth have made available high quality, undoped Ge/SiGe quantum wells, consisting of a pure strained Ge layer flanked by Ge-rich SiGe layers above and below. These quantum wells feature heavy hole carriers and a cubic Rashba-type spin-orbit interaction. Here, we describe progress toward realizing spin qubits in this platform, including development of multi-metal-layer gated device architectures, device tuning protocols, and charge-sensing capabilities. Iterative improvement of a three-layer metal gate architecture has significantly enhanced device performance over that achieved using an earlier single-layer gate design. We discuss ongoing, simulation-informed work to fine-tune the device geometry, as well as efforts toward a single-spin qubit demonstration.

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TYPE Conference Poster YEAR 2019
ScopusOSTIDOI

Weak anti-localization of two-dimensional holes in germanium beyond the diffusive regime

Nanoscale

Chou, C.T.; Jacobson, Noah T.; Moussa, J.E.; Baczewski, Andrew D.; Chuang, Y.; Liu, C.Y.; Li, J.Y.; Lu, Tzu-Ming L.

Gate-controllable spin-orbit coupling is often one requisite for spintronic devices. For practical spin field-effect transistors, another essential requirement is ballistic spin transport, where the spin precession length is shorter than the mean free path such that the gate-controlled spin precession is not randomized by disorder. In this letter, we report the observation of a gate-induced crossover from weak localization to weak anti-localization in the magneto-resistance of a high-mobility two-dimensional hole gas in a strained germanium quantum well. From the magneto-resistance, we extract the phase-coherence time, spin-orbit precession time, spin-orbit energy splitting, and cubic Rashba coefficient over a wide density range. The mobility and the mean free path increase with increasing hole density, while the spin precession length decreases due to increasingly stronger spin-orbit coupling. As the density becomes larger than ∼6 × 1011 cm-2, the spin precession length becomes shorter than the mean free path, and the system enters the ballistic spin transport regime. We also report here the numerical methods and code developed for calculating the magneto-resistance in the ballistic regime, where the commonly used HLN and ILP models for analyzing weak localization and anti-localization are not valid. These results pave the way toward silicon-compatible spintronic devices.

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TYPE Journal Article YEAR 2018
ScopusOSTIDOI
Results 26–50 of 69
Results 26–50 of 69