Superconducting films fabricated by high fluence Ga implantation in Si

Ga-rich layers in Si were fabricated by 80 keV Ga implantation through a 30 nm SiO₂ cover layer and subsequent rapid thermal annealing for 60 s in a temperature range between 500°C and 1000°C. Fluences of 2x10¹⁶cm^-2 and 4x10¹⁶cm^-2, leading to Ga peak concentrations of 8 at.% and 16 at.%, are chosen. Residual damage in the implanted layers and the Ga distribution were investigated by Rutherford-backscattering spectrometry in combination with ion channeling, cross-sectional electron microscopy and X-ray photoelectron spectroscopy. Temperature dependent Hall-effect measurements were carried out in order to determine the electrical properties of the implanted layers. It is shown that annealing at temperatures up to 800°C leads to the formation of poly-crystalline layers containing random distributed amorphous clusters. At the Si/SiO₂ interface a dense and narrow band of Ga-rich clusters is observed. For 4x10¹⁶cm^-2 the amount of mobile Ga is higher than for 2x10¹⁶cm^-2 and an increase of the cluster density at the Si/SiO₂ interface was found. Due to the higher cluster density for 4x10¹⁶cm^-2 this interface layer can become superconducting below 7 K with critical fields exceeding 9 T at optimized annealing conditions. Critical currents are above 1 kA/cm² and therefore this seems to be a possible material system for future microelectronic applications. After annealing at 900°C and above, the implanted layers are single crystalline and no amorphous precipitates were found.