PhotonDetectionProbability Simulation Method for CMOS SinglePhoton Avalanche Diodes Singlephoton avalanche diodes (SPADs) in complementary metaloxidesemiconductor (CMOS) technology have excellent timing resolution and are capable to detect single photons. The most important indicator for its sensitivity, photondetection probability (PDP), defines the probability of a successful detection for a single incident photon. To optimize PDP is a cost and timeconsuming task due to the complicated and expensive CMOS process. In this work, we have developed a simulation procedure to predict the PDP without any fitting parameter. With the given process parameters, our method combines the process, the electrical, and the optical simulations in commercially available software and the calculation of breakdown trigger probability. The simulation results have been compared with the experimental data conducted in an 800nm CMOS technology and obtained a good consistence at the wavelength longer than 600 nm. The possible reasons for the disagreement at the short wavelength have been discussed. Our work provides an effective way to optimize the PDP of a SPAD prior to its fabrication.

An ASIC for Discriminating Single Photon Detector Signal of HighSpeed Quantum Key Distribution System An ASIC is presented in this paper for discriminating signal from single photon detector (SPD) of highspeed quantum key distribution (QKD) system. The circuit is designed in 130 nm CMOS process. It receives and discriminates a small voltage pulse from a SPD, coinciding with a trigger signal and outputs the effective signal to next stage of QKD system. The pulse width of the voltage signal from SPD is less than 400 ps. The circuit mainly consists of bandgap reference, high speed comparator, delay chain and current mode logic (CML) driver. It should operate at a speed of 1.25 GHz. This work integrate all the frontend electronics for SPD into a chip. The area, stray capacitance and power consumption of the whole circuit are reduced. And then the whole receiver of QKD system can be integrated into a chip to improve performance.