Study Of High Speed Avalanche Photodiode For Optical Communication Over 50Gbps And Beyond

Optical communication has undergone huge development since the early twenty-first century.The human society has become an information explosion era.Facing with the increasing demand for information interaction,it is necessary for the optical communication system to enhance its abilities of transporting and processing.In the early 2000s,the requirements for optical chips were 4×10G bit/s.While this requirement rised suddenly to 4x25G bit/s in 2007.With the growing universalness of the fourth-generation network since 2014,the optical chips under 25 Gbps are no longer adequate for modern communication system.Therefore optical chips for over 40 Gbps or even 50 Gbps are now in urgent need.Avalanche photodiodes(APDs),benefiting from its huge internal gain,act as an important role in optical receiver and have been widely adopted in optical communication systems.In an APD,photons get absorbed in absorption region and transfer into photo-generated carriers.These carriers are drifted to the multiplication region by electric field force and trigger the impact ionization process.The impact ionization process last until all the carriers exit the multiplication region.Generally speaking,the impact ionization turns fiercer and gain increases as the volgates rises up.However,the response time is also prolonged correspondingly.On the other hand,if the voltage is decreased,the response time gets reduced but at the same time the avalanche gain will be lower,too.Therefore the APD commonly has a bottle-neck of gain-bandwidth-product(GBP).Traditional InP APD has the GBP limit of 80?120 GHz and InAlAs APD has the GBP limit of 105?160 GHz.Neither of these devices has the ability to acquire the speed over 40Gbps.Apart from the avalanche build-up time,there are other factors that restrict the high-speed development of APD as well such as RC constant,carrier transit time,effective k value an so on.Hence in this thesis,multiple priciples and methods will be explored to help APD to reach over 50 Gbps running.In this thesis,three-dimensional multiplication region will be first adopted to promote the bandwidth of APD.In order to support this new structure,3D Dead Space Multiplication Theory(DSMT)will be first fully developed and perfected.By analyzing the impact ionization in all different electric field lines and optimizing the distributions of E-field lines,the APD's response time can be reduced obviously.While studying the hole-trapping effect around the grading layer of an APD,the volatility of particles is first taken into consideration.Besides,the Schrodinger's Equation and its discrete resolving method are first introduced into the analysis of transmission coefficients.The correctional factor is proposed to combine the thermionic emission model and resonant tunneling model.This factor succeeds to integrate the new effect into the existing equivalent circuit model and produce a new model,with whose help the grading layer gets optimized and the speed gets promoted for?30%.Beyond these,in this thesis,the dynamic voltage method is also introduced to increase the GBP of an APD.By comparing all the bias forms,the best waveform is obtained to minimize the impulse tails.In addition to these,in this thesis,there are other methods that are elaborated and demonstrated.For example,two independent absorptions for APD can be utilized to optimize the carrier's transit time.Resonant cavity can be used to enhance the photon absorption for ultra-thin absorber,which is benefit for shorter transit time.Stibnide multiplication can be adopted to break through the restriction of GBP.All these methods above have been fully considered and the final optimal scheme has been concluded for realization of APDs functioning over 50 Gbps.