Epitaxial niobium nitride superconducting nanowire single-photon detectors

Superconducting nanowires used in single-photon detectors have been realized on amorphous or poly-crystalline films. Here, we report the use of single-crystalline NbN thin films for superconducting nanowire single-photon detectors (SNSPDs). Grown by molecular beam epitaxy (MBE) at high temperature on nearly lattice-matched AlN-on-sapphire substrates, the NbN films exhibit high degree of uniformity and homogeneity. Even with relatively thick films, the fabricated nanowire detectors show saturated internal efficiency at near-IR wavelengths, demonstrating the potential of MBE-grown NbN for realizing large arrays of on-chip SNSPDs and their integration with AlN-based $\chi^{(2)}$ quantum photonic circuits.