Design And Optimization Of High Responsivity And High Bandwidth Avalanche Photodiode

In the past few decades,Avalanche Photo Diodes（APDs）have been widely used in scientific research,medical,military,commercial and other fields.Since the 1980s,optical detection,fiber optic communication,imaging,laser ranging,and single photon detection have greatly promoted the continuous development of APD devices.How to further improve the response bandwidth and responsiveness of devices has become a major research focus at home and abroad.This thesis will focus on how to improve the response bandwidth of devices and design silicon based APD devices with high responsiveness and high response bandwidth.In order to improve the response bandwidth of APD devices,this thesis starts with conventional N+/PSUB APDs and P+/NWELL/PSUB APDs,and analyzes the performance of the two devices through TCAD simulation software.The results show that the two devices have low responsiveness and response bandwidth.A shallow slot isolation layer（STI）and interdigital electrodes were added to the P+/NWELL/PSUB APD and simulation analysis was conducted.The results showed that STI effectively prevented early breakdown of the device,and the device obtained a larger planar junction avalanche current.At the same time,the interdigital structure also shortened the carrier lateral transport distance,and reduced the device response time.At a 10V bias voltage,0.001 W/cm² light intensity,and 500 nm incident light wavelength,the 5P structure（P-type cross index of 5）3d B bandwidth reached 2.13GHz.Subsequently,the interdigital structure was optimized using carrier acceleration technology.The results showed that under the same incident light intensity and wavelength,when the voltage of cathode 1was 7V and the voltage of cathode 2 was 10V,the 3d B bandwidth of the same 5P structure reached 2.54GHz,increasing by 19.2%,additionally,the responsivity is 0.69A/W.In order to obtain APD devices with high responsiveness and high response bandwidth,this thesis designs a silicon based dual region avalanche photodiode.Firstly,it was demonstrated through software simulation that the virtual protection ring can concentrate high electric fields on the central plane junction.Then,the avalanche I-V characteristics,photocurrent response,quantum efficiency,and frequency response of dual avalanche region APD and single region APD in linear mode are simulated and compared.The results show that when the avalanche multiplication is significant,the photocurrent,quantum efficiency,and response bandwidth of the dual avalanche region APD are much higher than those of the single region APD.In addition,when the incident light wavelength is 480 nm,the intensity is 0.001W/cm²,the bias voltage of the DNW/PWELL junction is 16.8V,and the bias voltage of the N+/PWELL junction is13.7V,the bandwidth of the dual avalanche region APD reaches 1.15GHz,while the responsiveness is 14.7A/W.Finally,through simulation analysis,the effects of different device areas and PWELL concentrations on the performance of APD were deeply studied.The research shows that by reducing the area of the device,the output photoelectric current of the device decreases proportionally,i.e.,the responsiveness remains unchanged,while the response bandwidth increases.When the area of the dual region APD is reduced to half,and the dual junction bias voltage is 16.8V and 13.6V,respectively,the bandwidth is increased by 38%,reaching 1.96GHz;In addition,as the concentration of PWELL increases,the photocurrent output and frequency response ability of the device will both decrease.When the dual junction operating voltage is 0.95V_B（breakdown voltage）,the response at the concentration of 8×10¹⁷cm^-3 decreases by 0.51A/W compared to2×10¹⁷cm^-3,and the bandwidth decreases by 0.988GHz.