Niobium nitride based Josephson junctions with unoxidized silicon barriers

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Abstract
NbN based tunnel junctions with unoxidized amorphous silicon barriers and niobium counter electrodes have been investigated under various barrier preparation conditions. The barrier consists of Si:H sandwiched between two thin silicon passivation layers. The H2concentration of the sputtering gas was varied form zero to 75% and correlated with barrier height. Vmvalues at 2mV and 4.2K exceeding 50 mV for some junctions have been obtained. The effective barrier thickness and average barrier height have been varied and are correlated with current density. Junctions with critical current densities exceeding 104Amps/cm2have been fabricated. At 103Amps/cm2Vmvalues exceeding 40 mV have been measured. The high voltage I-V characteristics of some junctions have been analyzed using the Simmons model which gives an average barrier height exceeding 160 mV. Some junctions have been fabricated with sum gap voltages exceeding 4.1 mV using various electrode passivation techniques.