Superconductivity in silicon nanostructures

We present the findings of single-hole and pair-hole tunneling into the negative-U centres at the quantum well-δ-barrier interfaces that seems to give rise to the superconductivity observed in the silicon nanostructures prepared by short time diffusion of boron on the n-type Si(1 0 0) surface. These Si-based nanostructures represent the p-type ultra-narrow self-assembled silicon quantum wells, 2 nm, confined by the δ-barriers heavily doped with boron, 3 nm. The EPR and the thermo-emf studies show that the δ-barriers appear to consist of the trigonal dipole centres, B+-B-, which are caused by the negative-U reconstruction of the shallow boron acceptors, 2B0→ B+ + B-. Using the CV and thermo-emf techniques, the transport of two-dimensional holes inside SQW is demonstrated to be accompanied by single-hole tunneling through these negative-U centres that results in the superconductivity of the δ-barriers, which seems to be in frameworks of the mechanism suggested by E. Simanek and C.S. Ting (Sol. St. Commun. 32 (1979) 731; Phys. Rev. Lett. 45 (1980) 1213). The values of the correlation gaps obtained from these measurements are in a good agreement with the data derived from the temperature and magnetic field dependencies of the magnetic susceptibility, which reveal a strong diamagnetism and additionally identify the superconductor gap value