A superconducting proximity effect existing in a two-dimensional electron gas in the native inversion layer on a $p$-type InAs substrate has been confirmed. A supercurrent in the inversion layer was observed for the first time, in addition to an ac Josephson effect, with superconducting electrodes separated by 0.2-0.5 μm. The coherence lengths obtained coincide well with each other, both experimentally and theoretically. A junction with a metal gate electrode showed the controllability of the supercurrent by the gate voltage.

• Received 19 March 1985

DOI:https://doi.org/10.1103/PhysRevLett.54.2449