| The single photon detector based on the avalanche photodiode manufactured by the In Ga As P material system is mainly used for photon counting in the near-infrared band of 0.9-1.6?m.In Ga As/In P avalanche photodiode has a great advantage,which is biased above it's breakdown voltage with infinite gain,called Geiger mode.When a photon incident on the active area,it can trigger a self-sustainable avalanche,generating a detectable electric signal.Regarding the performance trade-off between photon detection efficiency(PDE)and dark count rate(DCR),a compromise can be made between these two parameters according to specific application requirements.At present,for thermoelectrically cooled fiber-coupled devices with a photosensitive surface diameter of 25?m,a dark count rate as low as 1 k Hz can be achieved at a detection efficiency of 20%.Although the uniformity of the device is critical for obtaining low timing jitter,it is currently possible to achieve a jitter of less than 50 ps.At the same time,a major breakthrough has been achieved in reducing the photon counting rate caused by afterpulsing.By using a 1 ns gating circuit,the afterpulsing probability is now only 1-5%at a repetition frequency of 50 MHz.The improvement of the material properties is a major challenge in the foreseeable future,therefore,in addition to the improvement of the device itself,the optimization of the external working circuit is also crucial to the above progress.Therefore,the design of integrated circuits matching the lab-made In Ga As/In P single photon avalanche diodes becomes a key issue.In order to study the photoelectric characteristics of In Ga As/In P SPADs developed by our group,the SPADs were characterized by a single-photon detector test system based on a field programmable gate array(FPGA).The clock frequency of the system can attain 100 MHz,the gate width can be as narrow as 1 ns,while the FPGA parameters are easy to adjust for increased flexibility of the system.At the same time,an optical test system has been built,which is compatible with both fiber-coupled and free-space devices,it plays a significant role in testing the performance of a single photon avalanche diode,and provides a guideline for the high-speed application of single-photon detectors.Based on the above test system,the PDE and DCR of SPADs are tested and characterized;In our experimental characterization,the SPADs were operated in the Geiger mode and thermoelectrically cooled;the FPGA system gate frequency was set to100 k Hz,the gate width 9 ns,and various bias voltages were applied.After the avalanche current triggered by an arriving photon was extracted,the avalanche signal was quickly quenched.The experimental results show that the PDE of the SPADs fabricated in our group can reach 30%at a temperature of-35?,but the DCR is still rather high,reaching 3×10~4k Hz.We also measured the dark count at different temperatures and the single-photon detection efficiency at different incident positions on the diode photosensitive surface.Analysis shows that the dark count has a strong dependence on temperature,and the non-uniformity of the internal electric field caused by the device doping and diffusion process seriously affects performance.Meanwhile,it is measured that the avalanche build-up time at room temperature is 1.0277 ns,and the afterpulsing probability decays exponentially as the hold time increases.Consequently,these experimental results are consistent with the theoretical model. |
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