Influence of the reactive gas mixture on the superconducting properties of nitrogen-doped aluminum thin films

Abstract

We present a correlation between disorder and superconducting properties in nitrogen-doped aluminum thin films, ranging from a few nitrogen impurities to the insulating limit due to AlN formation. Samples were deposited via reactive sputtering on (100) silicon substrates with native oxide at room temperature. Our findings show that adding nitrogen increases the superconducting critical temperature (Tc) compared to pure metal films. By varying the nitrogen/argon ratio up to 6 %, we observed a dome-like Tc behavior: 2 K at low concentrations, peaking at 3.3 K at intermediate concentrations, and then dropping as the samples become insulating (≈ 4.4 %). Increasing nitrogen raises resistivity and shifts the material from metallic to semiconductor-like behavior. Disorder impacts the upper critical field, starting at 0.2 T for low nitrogen content and reaching up to 3.2 T for nitrogen-rich samples with Tc = 2.2 K. Current-voltage curves reveal typical vortex dissipation, as expected for type II superconductors.