Fabrication, characterization and mechanical loading of Si/SiGe membranes for spin qubit devices

TL;DR

This paper reports the fabrication and characterization of Si/SiGe membranes designed for spin qubit devices, enabling strain and electric field control to enhance valley splitting and facilitate quantum information processing.

Contribution

It introduces a novel membrane platform for investigating valley splitting mechanisms and demonstrates fabrication of a spin-qubit shuttling device on these membranes.

Findings

Membranes can be metallized for electric field control

Elastic properties include linear elastic and buckling modes

Membranes support future valley mapping experiments

Abstract

Si/SiGe heterostructures on bulk Si substrates have been shown to host high fidelity electron spin qubits. Building a scalable quantum processor would, however, benefit from further improvement of critical material properties such as the valley-splitting landscape. Flexible control of the strain field and the out-of-plane electric field $\mathcal{E}_z$ may be decisive for valley splitting enhancement in the presence of alloy disorder. We envision the Si/SiGe membrane as a versatile scientific platform for investigating intervalley scattering mechanisms which have thus far remained elusive in conventional Si/SiGe heterostructures and have the potential to yield favourable valley-splitting distributions. Here, we report the fabrication of locally etched, suspended SiGe/Si/SiGe membranes from two different heterostructures and apply the process to realize a spin-qubit shuttling device on a membrane for future valley mapping experiments. The membranes have a thickness in the micrometer range and can be metallized to form a back-gate contact for extended control over the electric field. To probe their elastic properties, the membranes are stressed by loading with a profilometer stylus at room temperature. We distinguish between linear elastic and buckling modes, each offering mechanisms through which strain can be coupled to spin qubits.