The effect due to the tunneling of conduction electrons into the negative-$U$ centers at the disordered metal-semiconductor interfaces on the superconductivity of metal-semiconductor eutectic alloys is considered. Gorkov's formalism is used to calculate $T_c$ for (i) $n_I\ll 1$ and $\lambda \ne 0$, (ii) $\lambda =0\mathrm{}$. Where $n_I$ is the concentration of the pairing centers and $\lambda$ is the phonon-mediated electron-electron interaction in BCS theory. Our results can qualitatively explain the increase of $T_c$ in Al-Si, Al-Ge, and Be-Si eutectic alloys.

• Received 6 May 1980

DOI:https://doi.org/10.1103/PhysRevLett.45.1213