Characterization of superconducting germanide and germanosilicide films of Pd, Pt, Rh, and Ir formed by solid-phase epitaxy

Facilitated by recent advances in strained Ge/SiGe quantum well growth technology, superconductor–semiconductor hybrid devices based on group IV materials have been developed, potentially augmenting the functionality of quantum circuits. The formation of highly transparent superconducting platinum germanosilicide (PtSiGe) contacts to Ge/SiGe heterostructures by solid-phase epitaxy between Pt and SiGe has recently been reported, although with a relatively low critical temperature <1K. Here, we present a comparative study of the superconducting properties of Pt, Pd, Rh, and Ir germanides, along with an in-depth characterization of Ir(Si)Ge films formed by solid-phase epitaxy. For films fabricated under optimal epitaxy conditions, we report Tc = 3.4 K (2.6 K) for IrGe (IrSiGe). High-resolution scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy reveal that Ir reacts with Ge substrates to form a polycrystalline IrGe layer with a sharp IrGe/Ge interface.