InGaAs superconducting JFETs with Nb electrodes

The authors have fabricated InGaAs junction FETs with Nb source and drain electrodes with submicrometer spacings. The devices exhibit gate-controlled supercurrents as large as 8 mA/mm at 4.2 K. This value of controlled supercurrent is larger than any previously reported for superconducting field-effect devices. The channel material was n-type In/sub 0.53/Ga/sub 0.47/As, epitaxially grown by molecular beam epitaxy on InP substrates. Gate control was achieved using a p-n junction which was buried below the channel. This structure allowed the Nb superconductor to be deposited directly onto the freshly grown channel layer to insure a clean superconductor-semiconductor contact, which is essential for obtaining optimum superconducting properties. The superconducting electrodes were patterned by reactive ion etching.