NbN/AlN/NbN tunnel junctions fabricated at ambient substrate temperature

We have prepared NbN/AlN/NbN tunnel junctions at ambient substrate temperature. The AlN barriers are fabricated by reactive rf magnetron sputtering in the N/sub 2/ sputtering gas. We describe the electric and crystalline properties of the NbN and AlN thin films, and discuss tunneling characteristics and the properties of the junction interface. Even though the NbN/AlN/NbN trilayers were deposited without intentional heating, the junctions had a large gap voltage (V/sub g/=5 mV), sharp quasiparticle current rise (/spl Delta/V/sub g/=0.16 mV), and small subgap leakage current (V/sub m/=25 mV). A high critical current density (J/sub c/=8 KA/cm/sup 2/) is obtained in junctions with 1.5 nm thick AlN barriers. These results show that high-quality NbN/AlN/NbN tunnel junctions can be prepared at ambient substrate temperatures.<
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