Performance Analysis And Structural Optimization On Single Photon Avalanche Diode

Silicon Photomultiplier(SiPM)is gradually replacing Photomultiplier Tube(PMT)as a photodetector to detect photons at 420nm wavelength in positron emission computed tomography(PET)systems due to its high gain,excellent time resolution,and compatibility with magnetic fields.This paper aims to study the performance of single photon avalanche diode—the basic unit of SiPM,and design a SPAD with high photon detection efficiency and fast time response performance for detecting photons at 420nm wavelength.Firstly,the performance of the SPAD was analyzed.A simulation model of photon detection efficiency was established based on the principle of SPAD.Considering the randomness of the non-equilibrium carrier thermal diffusion,the Monte Carlo method was used to simulate the 2-D diffusion process of photo-generated carriers in the neutral region,and the 2-D model of time response was derived.The factors affecting the dark count and the afterpulsing and methods for suppressing these two noise were analyzed.Secondly,a new kind of SPAD was designed for detecting photons at 420 nm wavelength.A new guard ring fabrication process was proposed to effectively suppress edge breakdown while avoiding ion lateral diffusion loss fill factor.By the model proposed in this paper,the important structural parameters are optimized.The p-type neutral region thickness was designed to be 0.25?m and the n-well concentration was designed to be8e16/cm~3.The simulation results showed that photon detection efficiency under 2.5V over-bias voltage is 50.41%,and 99.9%of the avalanche signals are expected to occur within971 ps after the photon incidence.Finally,the SPAD processing was formulated.At the same time,the processing and device simulation of SPAD were carried out by using Silvaco simulation software to analyze the possible deviation between the performance simulation results and the actual situation.The results showed that,due to the existence of low electric field in the p-type neutral region,the photon detection efficiency and time response performance of the actual device will be better than the performance simulation results.