Nanosecond laser annealing: Impact on superconducting silicon on insulator monocrystalline epilayers

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-implanted with boron (2.5 × 1016 at./cm2, 3 keV). Superconductivity is discussed in relation to the structural, electrical, and material properties, a step toward 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 in the layer thickness and to the increase in the superconducting critical temperature Tc from zero (< 35 mK) to 0.5 K. This value is comparable with superconducting Si layers realized by gas immersion laser doping, where dopants are incorporated without introducing the deep defects associated with implantation. Superconductivity only appears when the annealed depth exceeds the initial amorphous layer induced by the boron implantation. Multiple subsequent anneals result in a more homogeneous doping with reduced amount of structural defects and increased conductivity. The quantitative analysis of Tc concludes on a superconducting–non-superconducting bilayer with an extremely low resistance interface. This highlights the possibility to efficiently couple superconducting Si to Si channels.