Theory of Andreev reflection in a junction with a strongly disordered semiconductor

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