Power law temporal dependence of InGaAs/InP SPAD afterpulsing

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 proportional to T-ho(-alpha) with alpha similar to 1.2 +/- 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.