Single-Photon Avalanche Diodes for the Near-Infrared Range: detector and circuit issues

Recently developed InGaAs/InP devices suitable as single-photon avalanche diodes (SPADs) in the near-infrared range provide good detection efficiency and low time jitter, together with fairly low dark-count rate at moderately low temperature. However, the overall performance is still severely limited by the afterpulsing effect (due to carriers trapped in deep levels during the avalanche and later released). Experimental studies and speculations aiming to improve the overall performance are here presented. The photon detection efficiency is characterized and the primary dark-count rate is investigated, taking into account thermal generation in the InGaAs layer (absorption layer) and trap-assisted tunneling in the InP layer (multiplication layer). Experimental investigations on the afterpulsing are reported. Improvements obtainable with existing devices by selecting proper operating conditions and circuit solutions are presented and discussed. In order to gain a better insight in the design of new devices, the effectiveness of trapping levels as a function of their location and of the electric field distribution is studied by computer simulation. The fundamental role played by the front-end circuits is assessed and demonstrated, in particular as concerns picosecond photon timing for a SPAD operating in gated-mode with ultrafast gate-on and gate-off transitions.