Excess voltage and resistance in superconductor-semiconductor junctions

We report the observation of excess voltage in Nb-${\mathrm{In}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As superconductor-semiconductor contacts (at large biases, the voltage in the superconducting state significantly exceeds that in the normal state). In addition, we describe an unusual temperature-dependent large-bias dynamic resistance, including a sudden increase as temperature decreases through the superconducting transition, a steady decrease with decreasing temperature below ${\mathit{T}}_{\mathit{c}}$, and a second smaller increase as temperature decreases through the onset temperature for the recently reported proximity-effect-induced pair current [A. Kastalsky et al., Phys. Rev. Lett. 67, 3026 (1991)]. These phenomena are discussed in terms of the rapidly evolving theory of superconductor-normal contacts with finite interface transmittance.