| In recent years,with the popularization and application of artificial intelligence,big data,and other technologies,the performance of ultrahigh-speed and large capacity optical transmission systems has been greatly tested.As a key component responsible for photoelectric conversion in optical communication systems,the development direction of photodetectors is to have both high-speed and high-power characteristics.The electrodes of high-speed photodetectors,as the key structure of high-speed photodetector chips,serve as an important bridge for signal transmission between the internal structure of the chip and external circuits.The high-speed performance,RF output power,and linear characteristics of the device are greatly influenced by the electrodes.Consequently,the reasonable design of the electrode structure of high-speed photodetectors plays a crucial role in the overall design scheme of high-speed photodetector chips.Theoretical and experimental research is carried out around the optimization and design of high-speed photodetector electrode structure and its transmission performance.The main research work and innovative results are as follows:1.The operating principle and performance parameters of high-speed photodetectors,as well as the design theory of electrode structure,are studied.An analysis is conducted on the electrode structures and array electrode structures of various photodetectors currently used,and a comparison is made between the current research status of the application of inductive peaking technology on electrodes at home and abroad2.A joint simulation design model for photodetector chips has been proposed.This model integrates the internal layer structure design model,equivalent circuit model,and electromagnetic model of electrodes to provide a simulation design process for the fabrication of photodetector chips.The chip layer structure parameters are obtained through computer simulation software.Using these parameters,the chip’s equivalent circuit model is established and the electromagnetic model of the electrode is introduced for joint simulation.A MUTC-PD with a size of 20μm is obtained,with a joint simulated bandwidth of 24.10GHz,which closely matches the device’s measured bandwidth of 22.5 GHz.3.A new electrode model has been established that is better suited for the actual preparation process.This model includes an insulating SiO2 layer between the InP substrate and the metal layer,with the metal layer being a Ti/Au double-layer metal stack structure.Simulation results indicate that the new electrode model has a minimum.transmission loss of-1.22 dB and a characteristic impedance of approximately 50Ω.The insulating SiO2 layer is 400 nm thick,the Ti layer is 100 nm thick,and the Au layer is 600 nm thick.Based on this new electrode model,three types of electrodes with different groove structures are proposed for etching on InP substrates.Simulations are conducted to evaluate the effects of different groove electrodes on device bandwidth performance.The bandwidth of the photodetector using a W-shaped groove electrode is 87.03GHz,the bandwidth of the photodetector using a rectangular groove electrode is 87.72 GHz,and the bandwidth of the photodetector using an elliptical groove electrode is 86.75 GHz.Compared to photodetectors without slot electrodes,photodetectors with slot electrodes have a bandwidth performance improvement of about 10%,as shown by the results.4.The electrode structure models of MUTC-PDs with different sizes have been designed.Inductive peaking technology has been adopted in these models.Based on the joint simulation design process of photodetector chips,the electrodes of MUTC-PDs with sizes of 12 μm,16μm,and 20 μm utilize inductive peaking technology.The disadvantage of large photodetectors being limited by large junction capacitors in frequency response and affecting device bandwidth performance is overcome by this design.The simulation results show that the bandwidth of the types of photodetector chips after peaking is 95.65 GHz,72.40 GHz,and 55.15 GHz,respectively.Compared with the bandwidth performance of the corresponding size device without inductive peaking,the device bandwidth with inductive peaking has increased by 41%,31%,and 27%,respectively.5.The process preparation of a 16 μm size MUTC-PD is completed,and its high-speed performance is tested.The experimental results show that devices with inductive peaking exhibit peaking phenomena,and the frequency response curves tend to increase.Concurrently,the device bandwidth is up to 26GHz. |
