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 degrees C and 1000 degrees C. Fluences of 2 x 10(16) cm(-2) and 4 x 10(16) cm(-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 degrees C leads to the formation of polycrystalline layers containing random distributed amorphous clusters. At the Si/SiO2 interface a dense and narrow band of Ga-rich clusters is observed. For 4 x 10(16) cm(-2) the amount of mobile Ga is higher than for 2 x 10(16) cm(-2) and an increase of the cluster density at the Si/SiO2 interface was found. Due to the higher cluster density for 4 x 10(16) cm(-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/cm(2) and therefore this seems to be a possible material system for future microelectronic applications. After annealing at 900 degrees C and above, the implanted layers are single crystalline and no amorphous precipitates were detected.