A P-I-N Structure Single-Photon Avalanche Diode Detector with Low Dark Count Rate
Objective Over the past few decades,single-photon detection technology has rapidly developed.Single-photon avalanche diode(SPAD)detectors operating in Geiger mode have advantages such as high sensitivity,fast response speed,and strong capability for single-photon detection.As a result,they have been widely used in optical sensing fields such as quantum communication,lidar,and fluorescence lifetime imaging.SPAD arrays compatible with CMOS technology have gained significant attention due to their high integration and miniaturization.In laser radar applications,SPADs are employed to receive returning photons.However,optical signals are susceptible to environmental factors like dust and weather conditions.The received light intensity might be at the single-photon level,and high dark count noise can degrade device performance.Considering the potential harm of short-wavelength lasers to human eyes,the design of SPAD devices with low dark counts and high photon detection probabilities has become a hot research direction.Methods The SPAD(Fig.1)employs a P-I-N diode structure,with the avalanche region located between the P-type drift region and the high-voltage N+buried layer.The P epitaxial layer serves as the intrinsic region,with P-trap guard rings and virtual guard rings surrounding the P-doped region to mitigate the impact of shallow trench isolation on dark count rates(DCR).The proposed SPAD devices with GRW of 3,4,5 μm are simulated based on 0.18 μm BCD technology to study the impact of GRW on device performance[Fig.2(a)].Simulation results show that the device can only work normally at GRW of 5 μm without a large edge electric field,and it will also cause the dark count to decrease.Figure 2(c)illustrates the 2D electric field distributions when STI extends into PW.Changing STI appropriately can hardly improve the electric field strength.Results and Discussions The I-V characteristic of the SPAD is firstly measured which exhibits avalanche breakdown voltage at around 56 V[Fig.3(c)],showing no difference to the TCAD simulation results(Fig.2).DCR measurement results[Fig.4(a)]show that the variation of DCR with Vex is not obvious and this value is more dependent on temperature changes.the data demonstrates excellent performance of 0.56 s-1·μm-2 at 23 ℃ and 5 V excess bias voltage.The PDP measurements(Fig.5)show that the peak PDP reaches 41.5％(600 nm)at Vex=5 V.Moreover,due to the wide depletion layer,there is a higher response sensitivity for near-infrared photons(780-940 nm)and PDP at 905 nm is more than 6％.Conclusions We propose an additional P-type injection enhanced P-I-N structure SPAD based on the SMIC 180 nm BCD process.The test results show that at Vex=5 V,the PDP peak of the SPAD reaches 41.5％,and the near-infrared PDP at the 905 nm wavelength is larger than 6％.At room temperature,it achieves a median DCR of 0.56 s-1·µm-2 and a very low afterpulsing probability＜1.2％when quenched passively with a dead time of 14 μs.
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