| Over the past fifty years,Avalanche photodetector(APD)have been widely used in commercial,military,and scientific fields.From the mid-1970s to the present,optical communication,imaging,and single-photon detection have been the main driving forces for research and development of APD.In the field of communications,APD stands out among semiconductor photodetectors because of its internal gain and high sensitivity,which can reduce the number of relay stations and amplifiers,thereby reducing system costs.In recent years,with the continuous development of high-speed and long-distance fiber-optic communication systems,people's requirements for device noise and frequency characteristics have become higher and higher.However,the application and development of traditional InP/InGaAs APD are limited by the gain bandwidth product,which is closely related to the excess noise of the material and the thickness of the multiplication region.Related research found that,replacing InP with the In0.52Al0.48As material as the multiplication region can reduce the excess noise of the device,and reducing the thickness of the multiplication region of the device can reduce the avalanche multiplication time of the carriers in the multiplication region and improve the bandwidth of the device.However,the edge electric field of such a thin multiplication layer is too high,which increases the possibility of device edge breakdown.In order to increase the bandwidth while solving the problems of higher electric fields at the edge of the device and dark currents,an avalanche photodiode with a triple-mesa and a partially depleted absorption layer is proposed in this paper.The structure is analyzed theoretically and optimized,which will achieve high speed and high stability of APD.The main research results and innovations of this paper are as follows:1.A triple-mesa structure SAGCM APD was designed and its edge electric field was optimized.We found that the triple-mesa structure can effectively confine the electric field to the center of the multiplication layer without the need to use selective doping technology or a complex guard ring structure.When the edge distance of mesa 2 is 5 ?m,the electric field at the edge of the multiplier layer is greatly reduced from 870 kV/cm to 440 kV/cm,and the dark current at 0.9 Vbr is reduced to 0.33 nA,which is only 1/3 of that of traditional double-mesa devices,thus improving the reliability and stability of the device.2.An APD based on the structure of a partially depleted absorption layer was designed.The partially depleted absorption layer is a mixed absorption layer composed of a P-type absorption layer and a depletion absorption layer,which is beneficial to improving the frequency response characteristics of the device.The effects of the ratio of the P-type absorption layer on the bandwidth under different total absorption layer thicknesses and different gains are calculated by simulation.Result found that the addition of a P-type absorption layer has the best bandwidth improvement for APD when the APD is at a gain of 3,the total absorption layer thickness is 0.8 ?m,and the ratio of the P-type absorption layer is 0.35.At this time,the bandwidth of the APD is 19.4 GHz,which is 21.25%higher than the avalanche photodetector using the traditional depletion absorption layer.3.An APD with triple-mesa and partially depleted absorption layer structure is proposed.This structure combines the advantages of a triple-mesa structure with a partially depleted absorber layer.The edge electric field of the designed APD multiplication layer is 358kV/cm lower than the traditional double-mesa APD,which effectively avoids edge breakdown when the multiplication layer is thin.When M=3,it can maintain a high bandwidth of 19.4 GHz and a multiplication responsiveness of 1.56 A/W,and the high speed and high stability can be satisfied.In addition,the influence of the incident light intensity on the APD bandwidth is analyzed.For the APD in this paper,the incident light intensity should be less than 2.2x104W/cm2. |
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