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

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 similar to 10 at. % by increasing the number of laser shots to 500. No superconductivity could be observed down to 40 mK for doping level below similar to 2 at. %. The critical temperature T(c) then increased steeply to reach similar to 0.6 K for c(B) similar to 8 at. %. No hysteresis was found for the transitions in magnetic field, which is characteristic of a type II superconductor. The corresponding upper critical field 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)].