We have fabricated and characterized at low temperature, down to 0.32 K, tunnel junctions made by a thin film of heavily doped silicon in contact with superconducting electrodes through Schottky barriers. Doped silicon films were chemical vapor deposited on silicon-on-insulator substrates and laterally dry etched in mesas. Aluminum or, alternatively, niobium contacts were deposited on the mesas. Below the superconducting critical temperature T_(c), an energy gap opens in the superconductor and the current-voltage characteristics become nonlinear and strongly sensitive to temperature changes. We have also characterized the heavily doped silicon in terms of the electron-phonon thermal decoupling by cooling the electron gas by means of aluminum-silicon-aluminum structures. With Nb electrodes, we have observed an anomaly of the electrical differential conductance at zero voltage and a larger electron dissipation, as a result of a less opaque barrier.
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