Research On Mechanism Of Dark Current In InGaAs/InP Avalanche Photodiode

In recent years,quantum satelite communication,active imaging,and other technologies have made great progress.Photodetectors are playing an important role as the core of receiving information.Compared with the traditional photomultiplier devices,avalanche photodetectors have many advantages in quantum efficiency,detection efficiency,and responsivity.In_0.53Ga_0.47As/InP avalanche photodiode(APD)is currently one of the best choices for infrared detectors which contributed by their matching lattice and coverage of the commonly used communication band of 1.55mm.However,the problem of high dark current has always been the most important reason for restricting its performance.At present,the mechanism of dark current in APD is not yet very clear.Therefore,the thesis mainly focuses on the research of the dark current in In_0.53Ga_0.47As/InP APD through the method of numerical simulation,aiming at providing theoretical guidance for reducing dark current and improving device performance.The main work and conclusions are as follows:1.Research on bulk dark current in planar In_0.53Ga_0.47As/InP APD.At first,a separate absorption grading charge multiplication(SAGCM)In_0.53Ga_0.47As/InP APD has been modeled by the Silvaco ATLAS device simulation software.Then the components of bulk dark current,containing the Shockley-Read-Hall(SRH)current,avalanche amplifica t io n current,Trap Assisted Tunneling(TAT)current,and Band-to-band Tunneling(BBT)current were separately extracted.Based on this,the effects of the doping concentration,trap concentration,and the thickness of the multiplication layer on dark current components are also researched.The low doping concentration in the multiplication layer is necessary for low dark current.TAT current is more dependent on the traps than the electric field.TAT current is positively related to the multiplication thickness and trap concentration.BBT current could be improved by reducing the electric field in the absorption layer.The electric field in the absorption layer must be less than 2×10⁵V/cm to avoid BBT,which becomes the dominant mechanism.2.Research on sidewall leakage current in mesa In_0.53Ga_0.47As/InP APD.Firstly,the surface leakage current caused by the surface defects in APD with mesa structure was studied in terms of theory.It was found that the surface charge in the In P multiplication layer and the surface recombination center in the In Ga As absorption layer are the main factors causing the surface leakage current.Based on this,the surface leakage current model was established.Secondly,starting from the factors affecting the surface leakage current,the mechanism of the surface leakage current is studied.It is concluded that part of the surface charge in the multiplication layer will participate in impact ionization.When the surface charge is sufficient and the bias voltage is high enough,the surface leakage current at the sidewall will generate and have a significant contribution to the dark current.The surface leakage current at the sidewall of the absorption layer is related to whether it is depleted.When the sidewall of the absorption layer is depleted,the surface leakage current at the sidewall increases with the surface recombination velocity,and increases obviously when the recombination velocity more than 1×10³cm/s.Based on this,the dark current of APDs with different mesa are compared.The results show that the difference of the structure will seriously affect the surface leakage current at the sidewall,resulting in different dark current.The surface leakage current at the sidewall in the double-mesa APD is the highest,while which in the multi-mesa APD is almost negligible.Finally,the effect of the terrace size on the dark current is studied.It's concluded that,in the triple-mesa APD,the smaller the terrace size,the higher the surface leakage current at the sidewall,so that the dark current of the triple-mesa APD depends heavily on the terrace size,while the dark current of multi-mesa APD hardly changes with the terrace size.