Side-gated, enhancement mode, InAs nanowire double quantum dot devices-toward controlling transverse electric fields in spin-transport measurements.

A double quantum dot system with a definitive transverse electric field in the plane of the sample is defined by combining a facile side-gating technique with enhancement mode InAs nanowires. Positive bias on the plunger gates enhance quantum dot segments along the nanowire, negative bias on barrier gates deplete regions, and situating gates biased at opposite polarities on opposing sides of the nanowire allows an electric field to be engineered. With sufficiently biased barrier regions stable bias triangle features are observed in the weak interdot coupling regime. The singlet-triplet energy splitting Δ ST in Pauli spin-blockaded features is studied as a function of an external magnetic field applied perpendicular to the sample plane. We interpret an apparent absence of mixing between singlet and triplet states as an indication that the spin-orbit field is oriented out of the sample plane due to the induced electric field. Finally, we discuss the potential of combining advanced gating architectures with enhancement mode nanowires to control the orientation of the spin-orbit field-a prospect that could enable multiple, nanowire-based spin-qubits to be operated on a single chip with a fixed-angle external magnetic field applied.

Achieving short high-quality gate-all-around structures for horizontal nanowire field-effect transistors.

We introduce a fabrication method for gate-all-around nanowire field-effect transistors. Single nanowires were aligned perpendicular to underlying bottom gates using a resist-trench alignment technique. Top gates were then defined aligned to the bottom gates to form gate-all-around structures. This approach overcomes significant limitations in minimal obtainable gate length and gate-length control in previous horizontal wrap-gated nanowire transistors that arise because the gate is defined by wet-etching. In the method presented here gate-length control is limited by the resolution of the electron-beam-lithography process. We demonstrate the versatility of our approach by fabricating a device with an independent bottom gate, top gate, and gate-all-around structure as well as a device with three independent gate-all-around structures with 300, 200, and 150 nm gate length. Our method enables us to achieve subthreshold swings as low as 38 mV dec-1 at 77 K for a 150 nm gate length.