A Modified Equivalent Circuit Model for High-Speed InGaAs/InAlAs Avalanche Photodiodes

In this paper, we establish a modified equivalent circuit model suitable for all bias conditions for high-speed InGaAs/InAlAs avalanche photodiodes (APDs). The model includes three mechanisms: the carrier transit time, the avalanche buildup time, and the RC time constant. The physical meaning of each component in it is elaborated in detail. Component parameters in it of the demonstrated APD are extracted by fitting the RF reflection parameters S22 and transmission parameters S21 measured at different bias voltages. To verify the accuracy and regularity of these parameters, some relevant finite element simulations and theoretical analyses are carried out. Values and regularities of these parameters are consistent with the results of finite element simulations and theoretical analyses. With the help of this model and these accurate parameters, impedance distribution and bandwidth limiting factors of the demonstrated APD are analyzed thoroughly. According to the above analysis results, the performance optimization scheme for the demonstrated APD is obtained.