ANDREEV REFLECTION AT SUPERCONDUCTING CONTACTS TO GAAS ALGAAS HETEROSTRUCTURES/

Highly transmissive ohmic contacts to the two-dimensional electron gas in GaAs/AlGaAs heterostructures have been made. For these contacts, w hich are of mum scale, a newly developed process of Ti/Sn evaporation and diffusion has been used. Devices consisting of these superconducti ng contacts combined with gate structures have shown clear evidence fo r the occurrence of Andreev reflection. Moreover a marked effect of th e gate voltage on the dV/dI-V characteristics has been found, which pr oves that superconductivity has been induced into the semiconductor.