Crossover from tunneling to metallic behavior in superconductor-semiconductor contacts

We describe current-voltage measurements on superconducting Nb/InGaAs junction field-effect transistors which reveal a crossover from tunneling-dominated to Andreev scattering-dominated transport at the superconductor-semiconductor contacts as Schottky barrier thickness decreases with increasing interfacial dopant concentration. These measurements are the first demonstration of such a crossover in a thin-film structure, and are of interest for investigations of hybrid superconductor-semiconductor devices, proximity effect boundary conditions, and transport in ohmic contacts to semiconductors.