In recent years, many applications have been proposed that require detection of light signals in the near-infrared (NIR) range with single-photon sensitivity and time resolution below 100 ps; notably laser ranging, biomedical imaging, quantum key distribution (QKD) and quantum information and communication experiments. The current state of the art in terms of timing resolution in the NIR range is a jitter below 20 ps achieved by superconducting nanowire single-photon detector (SNSPD). A more practical and compact alternative that does not require cryogenic cooling is represented by InGaAs/InP single-photon avalanche diodes (SPADs). Indeed, gated-mode SPADs can achieve a timing resolution below 50 ps at relatively high excess biases (above 7 V). However, despite their good performance in terms of photon detection efficiency, dark count rate and timing resolution, standard InGaAs/InP SPADs are limited by their afterpulsing noise to gated-mode operation, thus precluding their use in many applications.
Negative-feedback avalanche diodes (NFADs) are a special structure of InGaAs/InP SPADs where a monolitically-integrated quenching resistor is used to reduce the afterpulsing noise contribution hence allowing free-running operation. Here, we present our recent results on the characterization of the timing response of different NFAD detectors for temperatures down to 143 K that demonstrate how NFADs can achieve timing jitter down to 50 ps in an extended range of operating conditions.