Electrical Characterization of InAs Quantum Well Josephson Junctions with Ex-situ Al Contacts

Josephson junctions (JJs) are the fundamental building blocks of superconducting qubits and quantum circuits. Recent studies have highlighted the importance of voltage-tunable JJs, where an electrostatic gate modulates the carrier density in the semiconductor, thereby controlling the critical current (I_c). High-transparency Al/InAs contacts are typically achieved by epitaxial growth of Al on InGaAs/InAs quantum wells (QWs) at low temperatures. In this work, we investigate the superconducting proximity effect in Al/InAs QW JJs fabricated using an ex-situ Al deposition process. Prior to Al e-beam evaporation, in-situ ion milling with endpoint detection was employed to remove the top InGaAs barrier. We characterized the transport properties of the resulting JJs, specifically the I_c and normal resistance (R_n), for devices with varying channel widths and lengths. Depending on the junction geometry, we measured I_c values of 0.40–0.85 A/m and I_cR_n products of 30–125 µV. These results demonstrate a viable pathway toward realizing Al/InAs JJs without molecular beam epitaxy (MBE), enabling compatibility with scalable, wafer-level fabrication processes.