AlN-buffered superconducting NbN nanowire single-photon detector on GaAs

TL;DR

This study demonstrates that AlN buffer layers improve the superconducting and detection properties of NbN nanowire single-photon detectors on GaAs, significantly reducing dark counts and increasing efficiency, though with some thermal coupling challenges.

Contribution

The paper introduces AlN as an effective buffer layer for NbN SNSPDs on GaAs, enhancing critical temperature, current density, and detection efficiency compared to bare substrates.

Findings

AlN buffer increases critical temperature and current density of NbN films.

SNSPDs on buffered substrates show three orders of magnitude lower dark counts.

Detection efficiency on buffered substrates is about ten times higher at 900 nm.

Abstract

We investigated the suitability of AlN as a buffer layer for NbN superconducting nanowire single-photon detectors (SNSPDs) on GaAs. The NbN films with a thickness of 3.3 nm to 20 nm deposited onto GaAs substrates with AlN buffer layer, demonstrate a higher critical temperature, critical current density and lower residual resistivity in comparison to films deposited onto bare substrates. Unfortunately, the thermal coupling of the NbN film to the substrate weakens. SNSPDs made of 4.9 nm thick NbN films on buffered substrates (in comparison to detectors made from NbN films on bare GaAs) demonstrate three orders of magnitude lower dark count rates and about ten times higher detection efficiency at 900 nm being measured at 90% of the critical current. The system timing jitter of SNSPDs on buffered substrates is 72 ps which is 36 ps lower than those on bare substrate. However, a weaker thermal coupling of NbN nanowire to the buffered substrate leads to a latching effect at bias currents > 0.97 IC.