  We evaluate the microscopically relevant parameters for electrical transport
of hybrid superconductor-semiconductor interfaces. In contrast to the commonly
used geometrically constricted metallic systems, we focus on materials with
dissimilar electronic properties like low-carrier density semiconductors
combined with superconductors, without imposing geometric confinement. We find
an intrinsic mode-selectivity, a directional momentum-filter, due to the
differences in electronic band-structure, which creates a separation of
electron reservoirs each at the opposite sides of the semiconductor, while at
the same time selecting modes propagating almost perpendicular to the
interface. The electronic separation coexists with a transport current
dominated by Andreev reflection and low elastic back-scattering, both dependent
on the gate-controllable electronic properties of the semiconductor.
