Atomic-scale control of tunneling in donor-based devices

Xiqiao Wang,Jonathan Wyrick,Scott W Schmucker,Richard M Silver,Pradeep Namboodiri,Ranjit V Kashid,Andrew Murphy,M D Stewart

doi:10.1038/s42005-020-0343-1

Abstract

Atomically precise donor-based quantum devices are a promising candidate for solid-state quantum computing and analog quantum simulations. However, critical challenges in atomically precise fabrication have meant systematic, atomic scale control of the tunneling rates and tunnel coupling has not been demonstrated. Here using a room temperature grown locking layer and precise control over the entire fabrication process, we reduce unintentional dopant movement while achieving high quality epitaxy in scanning tunnelling microscope (STM)-patterned devices. Using the Si(100)2 × 1 surface reconstruction as an atomically-precise ruler to characterize the tunnel gap in precision-patterned single electron transistors, we demonstrate the exponential scaling of the tunneling resistance on the tunnel gap as it is varied from 7 dimer rows to 16 dimer rows. We demonstrate the capability to reproducibly pattern devices with atomic precision and a donor-based fabrication process where atomic scale changes in the patterned tunnel gap result in the expected changes in the tunneling rates.

Highlights

Precise donor-based quantum devices are a promising candidate for solid-state quantum computing and analog quantum simulations
Scanning tunneling microscope (STM)-patterned tunnel junctions lack the degree of tunability of top-gate defined tunnel barriers in conventional semiconductor heterostructures[6], it was shown by Pok[7] and Pascher et al.[8] that engineering the dimensions of the scanning tunnelling microscope (STM)-patterned nanogaps can affect the tunnel barriers and the tunnel rates in STM-patterned devices: even a ~1 nm difference in the tunnel gap separation can drastically change the tunnel barrier and transport properties in atomically precise Si:P devices[9]
We define “atomic-scale control of tunneling” as achieving the predicted response in the tunneling resistance relative to a given atomic-scale change in the tunneling gap. (For example, if the dimension of a tunnel gap is 11 dimer rows, and the gap is changed by 1 dimer row, there is an expected one order of magnitude change in tunneling resistance.) We mention here that reliable device metrology is possible at two stages, measuring the STM lithographic pattern dimensions on an atomically ordered surface and low-temperature transport measurements of the resulting device

Summary

Introduction

Precise donor-based quantum devices are a promising candidate for solid-state quantum computing and analog quantum simulations. We overcome previous challenges by uniquely combining hydrogen lithography that generates atomically abrupt device patterns[10,11] with recent progress in low-temperature epitaxial overgrowth using a locking-layer technique[12,13,14] and silicide electrical contact formation[15] to substantially reduce unintentional dopant movement. These advances have allowed us to demonstrate the exponential scaling of the tunneling resistance on the tunnel gap separation in a systematic and reproducible manner. SETs are exemplary structures because they are fundamental components in a number of quantum devices: they can function as DC charge sensors and are used in spin to charge conversion, qubit initialization, charge noise characterization, radio-frequency (RF)-SET reflectometry, and charge pumps

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Results

Conclusion