Atomic fluctuations lifting the energy degeneracy in Si/SiGe quantum dots

Electron spins in Si/SiGe quantum wells suffer from nearly degenerate conduction band valleys, which compete with the spin degree of freedom in the formation of qubits. Despite attempts to enhance the valley energy splitting deterministically, by engineering a sharp interface, valley splitting fluctuations remain a serious problem for qubit...

Lightly strained germanium quantum wells with hole mobility exceeding one million

We demonstrate that a lightly-strained germanium channel ("// = −0.41%) in an undoped Ge/Si0.1Ge0.9 heterostructure field effect transistor supports a 2D hole gas with mobility in excess of 1 × 106 cm2/Vs and percolation density less than 5 × 1010 cm−2. This low disorder 2D hole system shows tunable fractional quantum Hall effect at low density...

Wafer-scale low-disorder 2DEG in 28Si/SiGe without an epitaxial Si cap

We grow 28Si/SiGe heterostructures by reduced-pressure chemical vapor deposition and terminate the stack without an epitaxial Si cap but with an amorphous Si-rich layer obtained by exposing the SiGe barrier to dichlorosilane at 500 °C. As a result, 28Si/SiGe heterostructure field-effect transistors feature a sharp semiconductor/dielectric...

InSbAs two-dimensional electron gases as a platform for topological superconductivity

Topological superconductivity can be engineered in semiconductors with strong spin-orbit interaction coupled to a superconductor. Experimental advances in this field have often been triggered by the development of new hybrid material systems. Among these, two-dimensional electron gases (2DEGs) are of particular interest due to their inherent...

Quantum dot arrays in silicon and germanium

Electrons and holes confined in quantum dots define excellent building blocks for quantum emergence, simulation, and computation. Silicon and germanium are compatible with standard semiconductor manufacturing and contain stable isotopes with zero nuclear spin, thereby serving as excellent hosts for spins with long quantum coherence. Here, we...

Vanishing Zeeman energy in a two-dimensional hole gas

A clear signature of Zeeman split states crossing is observed in a Landau fan diagram of strained germanium two-dimensional hole gas. The underlying mechanisms are discussed based on a perturbative model yielding a closed formula for the critical magnetic fields. These fields depend strongly on the energy difference between the topmost and...

Low percolation density and charge noise with holes in germanium

Effect of quantum Hall edge strips on valley splitting in silicon quantum wells

We determine the energy splitting of the conduction-band valleys in two-dimensional electrons confined to low-disorder Si quantum wells. We probe the valley splitting dependence on both perpendicular magnetic field B and Hall density by performing activation energy measurements in the quantum Hall regime over a large range of filling factors....

Shallow and undoped germanium quantum wells: A playground for spin and hybrid quantum technology

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...