Silicon-coupled Josephson junctions and super-Schottky diodes with coplanar electrodes

Superconducting devices with coplanar electrodes have been fabricated using electron-beam lithography to define the smallest feature. The devices each consist of two Pb-In alloy electrodes, 20 µm wide, deposited on a clean, degenerately doped silicon substrate. The two electrodes are separated by a thin (100-300-nm) gap. Electron-beam lithography is used to define the gap, and sputter etching to remove the underlying alloy film. Depending on the width of the gap and the condition of the metal-semiconductor interface, these devices displayed either Josephson or super-Schottky diode behavior. The Josephson devices show a high degree of robustness and had products in the range 200-800 µV at 4.2 K. The super-Schottky diodes had current sensitivities S in the range 1000-1300 V^-1when measured at 4.2 K.