The first months of the project have been dedicated to the design and dimensioning of the detectors. Extensive simulations have been performed, and the performance achievable with the proposed approach has been quantified. The simulation results confirm that a waveguide-coupled device would allow highly efficient broadband photon detection, as predicted. In addition, the detector efficiency would be almost independent on the photon polarization, which is currently a major problem of normal-incidence detectors.
Furthermore, some innovative concepts to improve normal-incidence detectors have been tested by simulation, with very promising results. Relying on these calculation, the Partner Organization “Single Quantum BV” could demonstrate a device having a detection efficiency of 93%, which outperforms the current state of the art for NbTiN-based SNSPDs.
During four stays at the Partner Organization, the Marie Sklodowsca-Curie Fellow has learned much of the fabrication and characterization techniques of SNSPDs, and has transferred them to the Host Organization CEA Grenoble. Additional travel funding has been obtained by the Fellow through a French-Dutch grant (Partenariat Hubert Curien – Van Gogh), to enhance two-way exchanges between Grenoble and Delft.
Concerning the experimental work, GaN/AlN waveguides have been fabricated on sapphire, and NbN films have been deposited and characterized by different means (AFM, XRR, XRD, EPMA, XPS). The technology for the fabrication of normal-incidence SNSPDs has been succesfully transferred from the Partner to the Host organization by the Fellow, and working devices have been demonstrated. A characterization setup for device characterization in liquid helium has been developed and installed. In spite of the sub-optimal characterization temperature (4.2 K, while state-of-the-art results are obtained 2.5K or below) and the absence of a cavity (which limits the achievable efficiency to about 40%) the realized devices have efficiencies in excess of 20%, a very promising result. The developement of a cavity structure to approach and go beyond the state of the art is being developed.
Meanwhile, cooperations with different scientific organizations are being developed, in order to fabricate SSPDs on innovative supercounducting films. One notable example is the fabrication of SSPDs on CVD-deposited NbTiN, which would be a first worldwide demonstration.
