Boron distribution in two-phase superconducting silicon-on-insulator by atom probe tomography

Abstract

We investigate with Atom Probe Tomography (APT) the distribution of boron in a thin superconducting Silicon-On-Insulator film (33 nm) obtained by high-dose ion implantation (2.5 × 1016 at/cm2) and single-pulse laser melting (160 ns). Only 40% of the target dose was found in the superconducting film, indicating a severe loss of dopants upon fabrication. Besides, the extremely rapid growth of SiB3 precipitates during laser melting impedes the incorporation of active boron in the silicon lattice. Overall, SiB3 precipitates and hyperdoped silicon account for 5.0 × 1015 at/cm2 and 1.0 × 1016 at/cm2 of the retained dose, respectively. This partitioning of boron between the two phases is supported by the “isolated active dopants model,” which allowed to trace back the sheet resistance of the film from APT data. Lastly, the superconducting critical temperature of the present film (0.39 K) is relatively high in view of the computed concentration of active boron (2.3 × 1021 cm−3). This highlights the interplay between doping and strain relaxation in the establishment of superconductivity.