In this Topical Review, we survey the state-of-the-art of single photon detectors based on avalanche diodes fabricated in the InGaAsP materials system for photon counting at near infrared wavelengths in the range from 0.9–1.6 mm. The fundamental trade-off between photon detection efficiency and dark count rate can now be managed with performance that adequately serves many applications, with low dark count rates of ~ 1 kHz having been demonstrated at photon detection efficiencies of 20% for 25 mm diameter fiber-coupled devices with thermoelectric cooling. Timing jitter of less than 50 ps has been achieved, although device uniformity is shown to be essential in obtaining good jitter performance. Progress is also reported towards resolving the limitations imposed on photon counting rate by afterpulsing, with at least 50MHz repetition frequencies demonstrated for 1 ns gated operation with afterpulsing limited to the range of 1–5%. We also present a discussion of future trends and challenges related to these devices organized according to the hierarchy of materials properties, device design concepts, signal processing and electronic circuitry, and multiplexing concepts. Whereas the materials properties of these devices may pose significant challenges for the foreseeable future, there has been considerable\ud progress in device concepts and circuit solutions towards the present imperatives for higher counting rates and simpler device operation

The characterization and analysis of afterpulsing behavior in InGaAs/InP single photon avalanche diodes (SPADs) is reported for gating frequencies between 10 and 50 MHz. Gating in this frequency range was accomplished using a matched delay line technique to achieve parasitic transient cancellation, and FPGA-based data acquisition firmware was implemented to provide an efficient, flexible multiple-gate sequencing methodology for obtaining the dependence of afterpulse probability P ap on hold-off time T ho . We show that the detrapping times extracted from the canonical exponential fitting of P ap (T ho ) have no physical significance, and we propose an alternative description of the measured data, which is accurately fit with the simple power law behavior P ap / T À ho with $ 1.2 AE 0.2. We discuss the physical implications of this functional form, including what it may indicate about trap defect distributions and other possible origins of this power law behavior.

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