| The high-speed Si photodetector has the advantages of high efficiency,low cost,and integration with CMOS circuits.It is the core device of the "neck" of underwater wireless optical communication.This paper aims to improve the frequency response bandwidth of Si photodetectors,and conducts advanced research around bandwidth limiting factors,proposes a coupling equivalent model,and optimizes the photodetector structure.Finally,the requency response bandwidth of the high-speed Si photodetector reaches 400 MHz at 850 nm at-3 V.The main research contents of this article are as follows:1.The equivalent circuit model is a common method for studying high-speed photodetectors.However,this model only considers the effect of the RC time constant.However,when the device size is reduced or the material migration rate is relatively small,carrier transport becomes the main limiting factor for the high-speed performance of photodetectors.So,a new type of coupling equivalent circuit is proposed,including a traditional RC limiting circuit and a carrier transit RC limiting circuit,and connected through a voltage-controlled current source(VCCS).According to the Laplace transform of the carrier drift-diffusion equation and the continuity equation,the R and C in the carrier transit-limiting circuit are given practical physical meaning,which correspond to the carrier concentration,carrier lifetime,and diffusion component and so on.The equivalent circuit simulation results are consistent with the experimental measurement results.This coupled equivalent circuit provides an effective method for further analysis of the main bandwidth limiting factors of high-speed photodetectors and the optimization of subsequent device structures.2.Based on the simulation results of the coupled equivalent circuit,the Si PIN high-speed photodetector based on vertical structure is optimized and designed.Test results show that at-3V,the frequency response bandwidth reaches 400 MHz and the responsivity reaches 0.338 A/W@850 nm. |
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