Fabrication and Characterization of Boron-Implanted Silicon Superconducting Thin Films on SOI Substrates for Low-Temperature Detectors

In this paper, we discuss the characterization of boron-doped silicon superconducting thin films with a thickness of 70 nm made on silicon-on-insulator substrates by ion implantation and ultra-violet nanosecond laser annealing under nitrogen at atmospheric pressure. Two different ion-implanted doses of boron of 1 × 10¹⁶ and 2.5 × 10¹⁶ cm⁻² at 3 keV were tested in the study. Single laser pulses with energy densities in the range of 0.3–1.1 J/cm² were applied to activate the boron species in the silicon. A transition from partially (monocrystalline) to fully-melted (polycrystalline) silicon is observed when increasing the laser energy density. The critical temperature (T_c) and the upper critical magnetic field (B_c2) were measured for different samples. A maximum T_c of 100 mK was obtained in the monocrystalline phase of the silicon just before the transition into the polycrystalline phase. An obvious impact of the doping level and laser annealing energy density on the T_c values was observed. Different morphological and physical characterizations such as transmission electron microscopy, X-ray photoelectron spectroscopy and secondary ion mass spectrometry were performed and analyzed in order to compare the samples.