Research On High-speed Phototdetectors For Data Cneter

Driven by current high-speed communication application services such as big data,cloud computing,and 5G communication networks,the information-bearing capacity and transmission rate in the data network continue to climb to high rates and large capacity.As an important carrier in Internet application processing and computing,the data center is facing an upgrade to larger bandwidth and faster rate.However,due to its shortcomings,the traditional electrical interconnection is difficult to meet today’s data center transmission requirements,which bring huge opportunities for optical interconnection.Optical fiber communication technology has become an important development direction in data center interconnection schemes due to its advantages of long-distance,large capacity and high speed.With the large-scale deployment of data centers in recent years,the internal optical interconnection architecture is developing from 25Gbps/40Gbps to a higher rate architecture of 100Gbps/400Gbps,which promotes the data center optical module to iterate to a high rate.As the core device in the optical module,the photodetector plays a key role in converting the transmitted optical signal into an electrical signal.Therefore,studying a photodetector with high response speed and high quantum efficiency to transmit high-speed data,which has important value to the optical module for data center construction.PIN photodetectors,which have the characteristics of simple structure,suitable for large-scale production and integration,are widely used in current optical fiber communication systems.However,the inherent contradiction between bandwidth and quantum efficiency in their structure makes PIN photodetectors difficult to both acquire a higher response speed and a higher quantum efficiency.Therefore,in order to solve these problems,this paper optimizes the design and theoretical analysis of the structure of the PIN photodetector,so that it can effectively meet the high-speed data transmission requirements of the data center and high responsivity.The main research results and innovations of this paper are as follows:1.A high-speed and high-responsivity photodetector with a partially depleted absorption structure was designed based on doping optimization.In response to the contradiction of traditional photodetectors,in the non-depleted absorption region of partially depleted absorption photodetection(PDA),Gaussian doping is used to create a doping concentration gradient to introduce an electric field,so that photo-generated electrons can drift more quickly under the action of the electric field to move into the depletion region.In addition,a drift enhancement layer is added,which can balance the electron and hole drift time in the device,and at the same time,the junction capacitance of the device can be correspondingly reduced to obtain a higher response speed.In addition,in order to reduce the RC time effect,simulation and optimization of the device’s epitaxial layer structure and mesa size to reduce the junction capacitance.The device finally obtained through optimization has a bandwidth of up to 34.5 GHz with a-3V bias and a quantum efficiency of 67%at 1310 nm when the mesa diameter is 20μm.2.A dual-depletion region(DDR)photodetector with an integrated microlens is proposed.The coupling efficiency of the device and single-mode optical fiber are improved by integrating a lens on the InP substrate.The converging effect of the lens is also beneficial to reduce the size of the mesa of the device to reduce the junction capacitance of the photodetector,thereby alleviating the influence of the RC time constant on the bandwidth.Through the design and simulation of the lens,the converging ability of the microlens under different incident light and the light field distribution during converging are analyzed.The lens size is selected to be 120μm in diameter and 12μm in arch height.The photodetector integrated with this microlens has a bandwidth of 40.25GHz when the device mesa size is 15μm.3.A mushroom structured photodetector with an integrated reflection-focused lens is proposed.The lens’s reflective convergence ability is analyzed theoretically.The size parameter and focal length of the reflector,as well as the corresponding substrate thickness,are determined.We derive the quantum efficiency formula of the lens,and studies have shown that the introduction of microlens significantly improves the quantum efficiency of the device.The mushroom-shaped photodetector with a mesa diameter of 30μm and a middle absorber diameter of 16μm has a 3dB bandwidth of 40.9GHz at a-3V bias voltage and a quantum efficiency of 59.8%at a wavelength of 1310nm.Under the same conditions,the quantum efficiency of the photodetector without the reflector is less than 20%.4.The key process methods for preparing integrated microlens are explored,and the photoresist of lens shape is formed on the substrate by using photolithography hot-melt method,and the key process parameters for realizing the lens pattern are obtained.Taking into account the influence of exposure and development time on the lithographic lens pattern morphology during the experiment,by conducting comparative experiments,controlling relevant variables,and analyzing the experimental results,we successfully explored the process flow and related parameters of preparing microlens.