Control of threshold voltages in Si/SiGe quantum devices via optical illumination

TL;DR

This paper demonstrates how near-infrared optical illumination can precisely control and reset threshold voltages in Si/SiGe quantum devices at cryogenic temperatures, aiding in device stability and qubit operation.

Contribution

It introduces a systematic method to tune threshold voltages using optical illumination and presents a model explaining the underlying mechanism.

Findings

Threshold voltages can be set to match gate bias using illumination.

The threshold voltage remains stable and reproducible over a wide bias range.

Cryogenic illumination effectively resets quantum dot qubit devices after charging events.

Abstract

Optical illumination of quantum-dot qubit devices at cryogenic temperatures, while not well studied, is often used to recover operating conditions after undesired shocking events or charge injection. Here, we demonstrate systematic threshold voltage shifts in a dopant-free, Si/SiGe field effect transistor using a near infrared (780 nm) laser diode. We find that illumination under an applied gate voltage can be used to set a specific, stable, and reproducible threshold voltage that, over a wide range in gate bias, is equal to that gate bias. Outside this range, the threshold voltage can still be tuned, although the resulting threshold voltage is no longer equal to the applied gate bias during illumination. We present a simple and intuitive model that provides a mechanism for the tunability in gate bias. The model presented also explains why cryogenic illumination is successful at resetting quantum dot qubit devices after undesired charging events.