  Highly transmissive ballistic junctions are demonstrated between Nb and the
two-dimensional electron gas formed at an InAs/AlSb heterojunction. A
reproducible fabrication protocol is presented yielding high critical
supercurrent values. Current-voltage characteristics were measured down to 0.4
K and the observed supercurrent behavior was analyzed within a ballistic model
in the clean limit. This investigation allows us to demonstrate an intrinsic
interface transmissivity approaching 90%. The reproducibility of the
fabrication protocol makes it of interest for the experimental study of
InAs-based superconductor-semiconductor hybrid devices.
