Superconductor-semiconductor-superconductor planar junctions of aluminium on /spl delta/-doped gallium-arsenide

We have fabricated and characterized planar superconductor-semiconductor-superconductor (S-Sm-S) junctions with a high quality (i.e. low barrier) interface between an n/sup ++/ modulation doped conduction layer in MBE grown GaAs and in situ deposited Al electrodes. The Schottky barrier at the S-Sm interface was compensated by inserting several Si /spl delta/-doped layers above the conduction layer and close to the surface of the GaAs heterostructure. Below 1.2 K, the transition temperature of Al, the dc I-V curves of such S-Sm-S junctions with a wide and short GaAs channel exhibited the classic features of S-N-S junctions including subharmonic energy gap structure (SGS) and excess current (EC) due to Andreev reflections at the interfaces.