Influence of back reflections on the detection efficiency of superconducting nanowire single-photon detectors on GaAs

In an on chip quantum photonic device, which consists of quantum dots, a waveguide based logic and a SNSPD, the quantum dots are conveniently excited by a laser beam. Backside reflection of these excitation photons can lead to their detection by the SNSPD and therefore to malfunction of the whole photonic circuit. We studied the effect of back reflections at the substrate/sample-holder interface on the detection properties of NbN SNSPDs on a GaAs substrate with a 12 nm AlN buffer layer. The SNSPDs have a width of 120 nm, a thickness of 6 nm, a critical temperature of 9.9 K and a critical current density of 2.8 MA/cm² at 4.2K. Two identical SNSPDs were fabricated from the same NbN film at a distance of 50 μm from each other. One of these SNSPDs was covered with a bi-layer of 20 nm thick AlN and 110 nm thick Al to prevent top illumination, making it only sensitive to backscattered photons. Results of the study of the influence of backscattered photons on the optical response of the SNSPDs and possibilities to avoid them will be discussed in detail.