Transport properties of a superconductor-semiconductor ohmic contact

We report electrical measurements of a sandwich structure consisting of a niobium electrode in contact with a thin lightly doped n type InGaAs layer. The Bottom of the sandwich is a degenerate layer of n-type InGaAs used to collect the current. The semiconductor layers are grown by molecular beam epitaxy (MBE). These three layers are the essence of the proposed superconducting-base, semiconductor-isolated transistor (SUBSIT), lacking only the emitter tunnel junction. It could also form the basis for a superconducting FET type device. We have observed a resistance rise, beginning just below the transition temperature of the niobium, and continuing to at least 2 K. Nonlinear IV curves are also measured, and may be interpreted in some instances as space charge limited current flow.