Research On The Influence Of Interface State And Sidewall Surface State Of Ge/Si Avalanche Photodiode

Avalanche Photodiodes(APDs)are widely used in optical fiber communication,laser ranging and quantum imaging.Among them,Ge/Si APDs are favored by many scientific researchers due to their advantages of the absorption band of Ge is in the range of 800nm-1550nm,Si is mainly electron multiplication and easy to integrate with CMOS technology,and Ge is cheap.However,the interface states between Ge and Si greatly restrict the performance of Ge/Si APD.In addition,the mesa-type Ge/Si APD have a large sidewall surface area,leading to a large sidewall leakage current.Therefore,the influence of interface states on the performance and the influence of sidewall surface states on the sidewall leakage current in Ge/Si APD are discussed using simulation analysis in this paper.Firstly,the study of the influence of interface state of the planar Ge/Si APD on the performance were carried out in this paper.Silvaco software was used to model and simulate the planar Ge/Si APD considering the interface state.On this basis,the effects of interface-state type,interface-state density,and electrical trapping area on photo current,dark current,gain,frequency response,bandwidth,and gain-bandwidth product were studied.It is found that for the acceptor-type and donor-type interface states,the increase in density has no significant effect on photo current and dark current.Therefore,it hardly affects the gain,while the increase in capture area makes the gain decrease because of the increase in dark current.And when the density of acceptor-type interface state is less than 1×10¹²cm^-2,the breakdown voltage decreases significantly with the increase in the interface-state density,while the donor-type interface state does not affect the breakdown voltage.Then,for acceptor-type interface state,the increase in interface-state density makes the bandwidth decrease,while the increase in trapping area makes the bandwidth increase.For donor-type interface state,the increase in interface-state density and electron capture area have little effect.In addition,for the two interface states,the gain-bandwidth product decreases as the trapping area increases.Secondly,the research on the sidewall leakage current of the mesa-type Ge/Si APD was carried out.A mesa Ge/Si APD simulation model without guard ring structure were established firstly.On this basis,the influence of the surface charge density and the surface recombination velocity at the sidewall of the absorption layer and the multiplication layer on the sidewall leakage current were respectively discussed.It is found that only when the surface charge density of the multiplication layer exceeds a certain value inversely proportional to the applied bias voltage,the sidewall leakage current is positively correlated with the surface charge density,and the surface charge of the absorption layer does not affect the leakage current of the sidewall.Moreover,both the increase in the sidewall surface recombination velocity of absorption layer and multiplication layer will increase the sidewall leakage current,while the former occurs only when the device is punched through.Finally,the influence of the width of the guard ring on the dark current is studied.It is found that for APDs with many surface defects,the greater the surface charge density and surface recombination velocity,the increase in guard-ring width is more conducive to the reduction of dark current.For APDs with few surface defects,the guard-ring width has little effect.At the same time,the study also found that guard-ring width does not affect the bulk dark current,because the width of the charge layer does not affect the active area,and the optimal guard-ring width of the structure used under the set conditions is 2?m.