Theoretical And Experimental Study On Avalanche Photodiodes And Optimization Design

Avalanche photodiodes(APD)is one of key components in optical fiber communication systems.Compared with conventional p-n and p-i-n type photodetectors,APDs can provide higher sensitivity due to internal gain,and many researches have been focused on the performance improvement of APDs and optimization of device structures using III-V compound semiconductors.In recent years,the separated absorption,grading,charge,and multiplication(SAGCM)structure APDs have been extensively studied due to it is structural advantages.SAGCM InGaAs/InP APDs with high sensitivity and high multiplication gain are the most important components in modern optical communication receiver modules.However,the performance metrics are severely influenced by the structure parameter variations.Dark current and excess noise are important limiting factors for the APDs performance.In order to improve the APDs performance,we must optimize the structure design to reduce dark current and excess noise,and improve the signal-to-noise ratio.In this paper,by combining the experiments and theoretical simulations,the effects of structure parameter variations on the APDs performance have been studied,and the optimization design to reduce dark current and excess noise also has been proposed.The main content of this paper are introduced as follows:First,the measurements for APDs basic performance characteristics are performed and analyzed,including I-V characteristics,excess noise factor,and bandwidth measurement.From the I-V characteristics,we obtained the M-V characteristics,punch-through voltage and breakdown voltage.What's more,the effects of the power and wavelength of the incident light on the photo response characteristics also have been further measuered and analyzed.The relative intensity noise(RIN)introduced by the laser has been taken into consideration for the excess noise factor measurement,and the setup is based on the noisefigure meter HP8970 B.In addition,the limited factor for device bandwidth under different gain have been measured and analyzed from the frequency response measurement results.Second,the model for SAGCM InGaAs/InP APD has been performed based on the device simulator Silvaco ATLAS,and verified by comparing the measured current-voltage characteristics with the simulated data.Based on the simulated results,we have extracted the dark current components and given the analysis on the effects of different structure parameters on the dark current and its components,punch-through voltage and breakdown voltage.In addition,we also proposed the optimum charge sheet density range for different multiplication layer width according to our calculated results.Finally,a new APD structure has been proposed,which introduce longitudinal electric field and may achieve high gain and low noise characteristics from the simulated results.