Characterization of a gate-defined double quantum dot in a Si/SiGe nanomembrane

TL;DR

This paper demonstrates the fabrication and characterization of a double quantum dot in a Si/SiGe nanomembrane, showing controllable quantum states despite a buried interface, advancing silicon-based quantum device technology.

Contribution

It introduces a novel fabrication approach using a SiGe nanomembrane that eliminates misfit dislocations, enabling high-quality quantum dot formation with tunable properties.

Findings

Double quantum dot successfully formed despite buried interface

Tunable inter-dot tunnel coupling demonstrated

Singlet-to-triplet transition observed under magnetic field

Abstract

We report the fabrication and characterization of a gate-defined double quantum dot formed in a Si/SiGe nanomembrane. In the past, all gate-defined quantum dots in Si/SiGe heterostructures were formed on top of strain-graded virtual substrates. The strain grading process necessarily introduces misfit dislocations into a heterostructure, and these defects introduce lateral strain inhomogeneities, mosaic tilt, and threading dislocations. The use of a SiGe nanomembrane as the virtual substrate enables the strain relaxation to be entirely elastic, eliminating the need for misfit dislocations. However, in this approach the formation of the heterostructure is more complicated, involving two separate epitaxial growth procedures separated by a wet-transfer process that results in a buried non-epitaxial interface 625 nm from the quantum dot. We demonstrate that in spite of this buried interface in close proximity to the device, a double quantum dot can be formed that is controllable enough to enable tuning of the inter-dot tunnel coupling, the identification of spin states, and the measurement of a singlet-to-triplet transition as a function of an applied magnetic field.