612 research outputs found
Palladium gates for reproducible quantum dots in silicon
We replace the established aluminium gates for the formation of quantum dots
in silicon with gates made from palladium. We study the morphology of both
aluminium and palladium gates with transmission electron microscopy. The native
aluminium oxide is found to be formed all around the aluminium gates, which
could lead to the formation of unintentional dots. Therefore, we report on a
novel fabrication route that replaces aluminium and its native oxide by
palladium with atomic-layer-deposition-grown aluminium oxide. Using this
approach, we show the formation of low-disorder gate-defined quantum dots,
which are reproducibly fabricated. Furthermore, palladium enables us to further
shrink the gate design, allowing us to perform electron transport measurements
in the few-electron regime in devices comprising only two gate layers, a major
technological advancement. It remains to be seen, whether the introduction of
palladium gates can improve the excellent results on electron and nuclear spin
qubits defined with an aluminium gate stack
Observation of the single-electron regime in a highly tunable silicon quantum dot
We report on low-temperature electronic transport measurements of a silicon
metal-oxide-semiconductor quantum dot, with independent gate control of
electron densities in the leads and the quantum dot island. This architecture
allows the dot energy levels to be probed without affecting the electron
density in the leads, and vice versa. Appropriate gate biasing enables the dot
occupancy to be reduced to the single-electron level, as evidenced by
magnetospectroscopy measurements of the ground state of the first two charge
transitions. Independent gate control of the electron reservoirs also enables
discrimination between excited states of the dot and density of states
modulations in the leads.Comment: 4 pages, 3 figures, accepted for Applied Physics Letter
Anisotropic Pauli spin blockade in hole quantum dots
We present measurements on gate-defined double quantum dots in Ge-Si
core-shell nanowires, which we tune to a regime with visible shell filling in
both dots. We observe a Pauli spin blockade and can assign the measured leakage
current at low magnetic fields to spin-flip cotunneling, for which we measure a
strong anisotropy related to an anisotropic g-factor. At higher magnetic fields
we see signatures for leakage current caused by spin-orbit coupling between
(1,1)-singlet and (2,0)-triplet states. Taking into account these anisotropic
spin-flip mechanisms, we can choose the magnetic field direction with the
longest spin lifetime for improved spin-orbit qubits
Depletion-mode Quantum Dots in Intrinsic Silicon
We report the fabrication and electrical characterization of depletion-mode
quantum dots in a two-dimensional hole gas (2DHG) in intrinsic silicon. We use
fixed charge in a SiO/AlO dielectric stack to induce a 2DHG at the
Si/SiO interface. Fabrication of the gate structures is accomplished with a
single layer metallization process. Transport spectroscopy reveals regular
Coulomb oscillations with charging energies of 10-15 meV and 3-5 meV for the
few- and many-hole regimes, respectively. This depletion-mode design avoids
complex multilayer architectures requiring precision alignment, and allows to
adopt directly best practices already developed for depletion dots in other
material systems. We also demonstrate a method to deactivate fixed charge in
the SiO/AlO dielectric stack using deep ultraviolet light, which
may become an important procedure to avoid unwanted 2DHG build-up in Si MOS
quantum bits.Comment: Accepted to Applied Physics Letters. 5 pages, 3 figure
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