Shadow-wall lithography of ballistic superconductor\u2013semiconductor quantum devices

Sebastian Heedt,Michał P Nowak,May An Y Van De Poll,Sasa Gazibegovic,Nick De Jong,Nick Van Loo,Mark Ammerlaan,Erik P A M Bakkers,Francesco Borsoi,Kongyi Li,Ghada Badawy,Grzegorz P Mazur,Jie Shen,Kevin Van Hoogdalem,Pavel Aseev,Svetlana Korneychuk,Marina Quintero-Pérez,Alexandra Fursina,Leo P Kouwenhoven

doi:10.1038/s41467-021-25100-w

Abstract

The realization of hybrid superconductor–semiconductor quantum devices, in particular a topological qubit, calls for advanced techniques to readily and reproducibly engineer induced superconductivity in semiconductor nanowires. Here, we introduce an on-chip fabrication paradigm based on shadow walls that offers substantial advances in device quality and reproducibility. It allows for the implementation of hybrid quantum devices and ultimately topological qubits while eliminating fabrication steps such as lithography and etching. This is critical to preserve the integrity and homogeneity of the fragile hybrid interfaces. The approach simplifies the reproducible fabrication of devices with a hard induced superconducting gap and ballistic normal-/superconductor junctions. Large gate-tunable supercurrents and high-order multiple Andreev reflections manifest the exceptional coherence of the resulting nanowire Josephson junctions. Our approach enables the realization of 3-terminal devices, where zero-bias conductance peaks emerge in a magnetic field concurrently at both boundaries of the one-dimensional hybrids.

Highlights

The realization of hybrid superconductor–semiconductor quantum devices, in particular a topological qubit, calls for advanced techniques to readily and reproducibly engineer induced superconductivity in semiconductor nanowires
The native oxide that forms during the ex-situ processing is removed prior to the deposition of the superconductor. Another recent study employed growth chips with bridges and trenches that act as selectively shadowing objects during the evaporation of a superconductor[27]. Common to those methods is that the hybrid nanowires are removed from the growth substrate following the evaporation and undergo several post-interface fabrication steps such as alignment via scanning electron microscopy (SEM), electron-beam lithography involving resist coating, or etching
There, the closing and reopening of the induced gap are accompanied by the emergence of delocalised Majorana bound states (MBS), hallmarked by zero-bias peaks (ZBPs) at both boundaries of the hybrid nanowire[20]

Summary

Introduction

The realization of hybrid superconductor–semiconductor quantum devices, in particular a topological qubit, calls for advanced techniques to readily and reproducibly engineer induced superconductivity in semiconductor nanowires. Our approach is based on the deposition of superconducting thin films at a shallow angle onto semiconducting nanowires, which have been selectively placed on substrates with pre-patterned gates and shadow-wall structures.

Results

Conclusion