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A key challenge in fabrication of hybrid semiconductor-superconductor devices is forming highly transparent contacts between the active electrons in the semiconductor and the superconducting metal. It has been shown that a near perfect interface and a highly transparent contact can be achieved using epitaxial growth of aluminum on InAs nanowires [1]. Recently, this method was extended to two-dimensional systems and epitaxial aluminum on top of our near-surface InAs 2DESs were grown [2]. Quantum devices fabricated by selective etching of Al exhibited unprecedented quality for hybrid superconductor-semiconductor weak links. This has sparked a great deal of interest in low power classical and quantum computation as gate-controlled properties of the semiconductor allows scaling of such devices. In this work, we present recent progress in optimization of the growth of Al on InAs near surface quantum wells. We show the growth of InGaAs layers on top of InAs facilitates lower strain energy at the interface with Al and results in a flat and smooth growth allowing ultra thin superconducting Al films. We further extend this work to growth of higher Tc superconductors (such as Nb) on these thin film Al and compare the results to direct growth of these superconductors.
InAs is a particularly interesting material as it has strong spin orbit coupling that can lead to engineering novel states such as topological superconductivity. However, this method can be extended to topological insulators (in-situ growth of superconductor) and silicon for superconducting qubits. We discuss the challenges and our preliminary results in these areas. These exciting developments might lead to a number of useful applications ranging from novel low-power classical to quantum computing.

[1] P. Krogstrup et al. Nature Materials (2015)
[2] J. Shabani et al. Phys Rev B (2016)"