Low-temperature transition to a superconducting phase in boron-doped silicon films grown on (001)-oriented silicon wafers

Abstract

We report on a detailed analysis of the superconducting properties of boron-doped silicon films grown along the 001 direction by gas immersion laser doping. The doping concentration ${c}_{B}$ has been varied up to $\ensuremath{\sim}10\text{ }\text{at}\text{.}\text{ }%$ by increasing the number of laser shots to 500. No superconductivity could be observed down to 40 mK for doping level below $\ensuremath{\sim}2\text{ }\text{at}\text{.}\text{ }%$. The critical temperature ${T}_{c}$ then increased steeply to reach $\ensuremath{\sim}0.6\text{ }\text{K}$ for ${c}_{B}\ensuremath{\sim}8\text{ }\text{at}\text{.}\text{ }%$. No hysteresis was found for the transitions in magnetic field, which is characteristic of a type II superconductor. The corresponding upper critical field ${\ensuremath{\mu}}_{o}{H}_{c2}(0)$ was on the order of 1000 G, much smaller than the value previously reported by Bustarret et al. [E. Bustarret et al., Nature (London) 444, 465 (2006)].