Nanosecond Laser Annealing: impact on superconducting Silicon on Insulator epilayers

TL;DR

This study demonstrates that nanosecond laser annealing of heavily boron-doped silicon on insulator layers induces superconductivity, with properties tunable by annealing energy and repetitions, advancing large-scale integration of superconducting silicon.

Contribution

It introduces a novel laser annealing process to create superconducting silicon layers with controlled properties, avoiding deep defects typical of traditional doping methods.

Findings

Superconductivity appears when annealed depth exceeds initial amorphous layer.

Higher annealing energy increases layer thickness and critical temperature.

Multiple anneals improve doping homogeneity and conductivity.

Abstract

We present superconducting monocrystalline Silicon On Insulator thin 33 nm epilayers. They are obtained by nanosecond laser annealing under ultra-high vacuum on 300 mm wafers heavily pre-implantated with boron ($2.5\times \,10^{16}\, at/cm^2$, 3 keV). Superconductivity is discussed in relation to the structural, electrical and material properties, a step towards the integration of ultra-doped superconducting Si at large scale. In particular, we highlight the effect of the nanosecond laser annealing energy and the impact of multiple laser anneals. Increasing the energy leads to a linear increase of the layer thickness, and to the increase of the superconducting critical temperature $T_c$ from zero ($<35\, mK$) to $0.5\,K$. This value is comparable to superconducting Si layers realised by Gas Immersion Laser Doping where the dopants are incorporated without introducing the deep defects associated to implantation. Superconductivity only appears when the annealed depth is larger than the initial amorphous layer induced by the boron implantation. The number of subsequent anneals results in a more homogeneous doping with reduced amount of structural defects and increased conductivity. The quantitative analysis of $T_c$ concludes on a superconducting/ non superconducting bilayer, with an extremely low resistance interface. This highlights the possibility to couple efficiently superconducting Si to Si channels.