THEORY OF ANDREEV REFLECTION IN A JUNCTION WITH A STRONGLY DISORDEREDSEMICONDUCTOR

We study the conduction of a normal-metal-semiconductor-superconductor junction, where the semiconductor is strongly disordered. The differe ntial conductance d1/dV of this, structure is predicted to have a shar p peak at V=0. Unlike the case of a weakly disordered system, this fea ture persists even in the absence of an additional (Schottky) barrier on the boundary. The zero-bias conductance of such a junction is small er only by a numerical factor than the conductance in the normal state G(N). Implications for experiments on gated heterostructures with sup erconducting leads are discussed.