Improving characterization capabilities in new single-photon avalanche diode research.

Many novel and promising single-photon avalanche diodes (SPADs) emerged in recent years. However, some of them may demonstrate a very high dark count rate, even tens of megahertz, especially during the development phase or at room temperature, posing new challenges to device characterization. Gating operation with a width of 10 ns can be used to suppress the dark counts not coincident with the photon arriving time. However, as a side effect of the fast-gating operation, the gating response could be much higher than the avalanche signal and is usually removed by various circuit-based cancellation techniques. Here, we present an alternative method. A high-speed digital storage oscilloscope (DSO) is used to extract the weak avalanche signals from the large gating response background by waveform subtraction in software. Consequently, no complex circuit and precise tuning for each SPAD are needed. The avalanche detection threshold can be reduced to 5% of the full vertical scale of the DSO or 5 mV, whichever is greater. The timing resolution can be better than 2 ps for typical avalanche signals. Optical alignment and calibration are easy. The feasibility of on-wafer test with an RF probe station is discussed. All the advantages and features listed above make this method very useful in new SPAD research.