Reflectionless tunneling in planar Nb/GaAs hybrid junctions

Reflectionless-tunneling was observed in Nb/GaAs superconductor/semiconductor junctions fabricated through a two-step procedure. First, periodic δ-doped layers were grown by molecular beam epitaxy near the GaAs surface, followed by an As cap layer to protect the surface during ex-situ transfer. Second, Nb was deposited by dc-magnetron sputtering onto the GaAs(001) 2× 4 surface in-situ after thermal desorption of the cap layer. The magnetotransport behavior of the resulting hybrid junctions was successfully analyzed within the random matrix theory of phase-coherent Andreev transport. The impact of junction morphology on reflectionless tunneling and the applicability of the fabrication technique to the realization of complex superconductor/semiconductor mesoscopic systems are discussed. a)Electronic mail: [email protected] b)Also with Institut de Physique Appliquee, Ecole Polytechnique Federale de Lausanne, Switzerland c)Also with Dipartimento di Fisica, Università di Trieste, I-34127 Trieste, Italy