Solid state diffusion for atomically sharp interfaces in semiconductor-superconductor hybrid structures
The emerging field of superconducting optoelectronics has the potential to impact future quantum processing, communication and encryption. Hybrid light-emitting diodes exhibit emission of entangled photons enhanced by the superconducting state, while novel superconductor (Su) based lasers and quantum light sources have been proposed. Despite the amount of research done in semiconductor (Se) p-n physics and superconductivity, the practical integration between these two field of research is poor mainly due to the weak control of high quality Se/Su interfaces. 
This project proposes to overcome these limitations with a new fabrication technique, based on the metallic diffusion of metals in Se nanowires (NWs), for the realization of atomically sharp Su/Se interfaces with an epitaxial relationship.
Starting from a material search I will then investigate the Al (Tc~1K) diffusion into n-doped InAs NWs as well as V and Nb (all Tc>5 K) diffusion into InAs, Si, Ge and GAs NWs. The band structures and resulting contact types (Schottky or Ohmic) of the different material systems will be studied numerically and tested at cryogenic temperatures to find the best material combination. Doping of the nanowires will be tuned to demonstrate superconducting correlations in both p- and n-doped NWs, an essential step for the realization of superconducting diodes. Diffusion through in-situ (S)TEM heating experiments will allow me to control the Su/Se/Su junctions up to the ultimate limit of few nanometers. These ultra-short JJs will allow to enhance the superconducting correlations. Ballistic transport will be probed down to ultra-low temperatures (~10 mK). and the quantification of the mean free path and the quality of the interfaces will take place. By embedding these ultra-short JJs in a superconducting quantum interference device I will be able to control the intensity supercurrent as well as achieving ultimate magnetic-sensitivity ready for novel technological applications.