Characterization of MBE-grown Ge/SiGe Josephson junctions for voltage tunable qubits

Planar Josephson junctions are fabricated using undoped germanium quantum wells (Ge-QWs) on top of a 2.5-μm tall mesa. The compressively stained Ge-QW and relaxed silicon germanium (SiGe) barrier material is grown using Molecular Beam Epitaxy (MBE) and has a carrier mobility greater than 60,000 cm²/Vs with a hole density less than 1x10¹² cm^-2. The SiGe mesa is necessarily created to isolate the lossy epitaxial layers from the rest of the circuit and is one of the essential elements needed to create a voltage tunable SiGe transmon qubit. This presentation will discuss the fabrication and preliminary characterization of electrostatically gated Josephson junction devices.