Research On Capacitance Characteristics Of High Speed PIN Photodetector In Optical Communication

With the continuous acceleration of the informationization process in modern society,the network traffic has increased "explosive",and the demand for communication bandwidth and capacity has become increasingly prominent.High-speed fiber-optic communication technology has become a rising concern as the main method to tackle these problems successfully.The photodetector is a key component of the high-speed fiber-optic communication system.The PIN photodetector is relatively simple for its preparation process,suitable for mass production and integration,and long-wavelength fiber-optic communication.It has a wide range of applications in the system.The main factors that limit the high-speed performance of PIN photodetectors are carrier transit time,RC time constant and charge trapping effect of heterojunction.The RC time constant mainly restricts the response speed of photodetectors at high frequencies.The high-speed performance of photodetectors is limited by the capacitance characteristics,so the capacitance characteristics become one of the important considerations for the design of high-speed PIN photodetectors.In addition,in the field of optoelectronic integration,the capacitance parameters are essential for establishing a unified PIN photodetector equivalent circuit model that can analyze signal noise characteristics.It is necessary to study the capacitance characteristics of PIN photodetectors.This dissertation focuses on the capacitive characteristics of PIN photodetectors.The main research contents and innovations are as follows:1.The theoretical model of PIN photodetectors capacitance characteristics based on carrier classification is established.In this dissertation,based on the differential capacitance theory of PN junction,the carrier motion analysis inside the PIN photodetector,especially the stacking model of photogenerated carriers,is considered,and the relationship between saturation performance and capacitance characteristics of the device is considered.Based on the carrier categorization model of PIN photodetectors capacitance characteristics,the model can better reflect the influence of carrier motion on the capacitance characteristics,and better explain the variation trend of capacitance characteristics under different working conditions.2.The PIN photodetector capacitance characteristic measurement system based on AC bias analysis and equivalent circuit fitting were designed and built.Designs and builds the measurement system based on AC bias to measure the capacitance characteristics of PIN photodetectors under different conditions.The measurement results are consistent with the ATLAS software simulation results.At the same time,the measurement system based on the equivalent circuit fitting was designed and built to measure the capacitance characteristics of the PIN photodetector.Through comparative analysis,the measurement results obtained by the two measurement methods are consistent in the trend and value.and the change trend of the capacitance characteristics is consistent with the theoretical model proposed by the dissertation.3.The relationship between capacitance and incident light power,reverse bias,absorption layer thickness and area were studied.Based on measurement and simulation data,this dissertation uses the established theoretical model to explain the relationship between the capacitance characteristics of PIN photodetectors and incident light power,reverse bias,absorption layer thickness and area.These relationships are beneficial to the design and application of high saturation and high speed PIN photodetectors.4.Through simulation and measurement results,it is verified that the capacitance characteristics of PIN photodetectors increase with the incident light power first and then decrease.The downward trend of the capacitance characteristics of PIN photodetectors has been found,which is of great significance for perfecting the theoretical model of capacitance characteristics.5.The relationship between the light-intensity-dependent capacitance and the DC saturation characteristics of the PIN photodetector was found.The capacitance of the reaching its maximum value near the saturation point.Through simulation and measurement,the correctness of the relationship is demonstrated,and a method for measuring the saturation performance of the device with the change of the incident optical power is proposed.