Current transport at Schottky barriers is of particular interest for spin injection and detection in semiconductors. Here, electrodeposited Ni-Si contacts are fabricated and the transport mechanisms through the formed Schottky barrier are studied. Highly doped Si is used to enable tunneling currents. I-V, C-V and low-temperature I-V measurements are performed and the results are interpreted using tunneling theory for Schottky barriers and recent models for spatially distributed barrier heights. It is shown that, contrary to the case of lowly doped Si where thermionic emission dominates, tunneling is the dominant mechanism for reverse and low forward bias for highly doped Si. An exponential reverse bias I-V behavior with negative temperature coefficient is reported. An explanation can be found on the rapid decrease of the reverse bias I-V slope with temperature predicted by Padovani and Stratton for thermionic field emission in conjunction with the increase of the Schottky barrier height with temperature suggested for spatially distributed barrier heights.