This study focuses on the dynamic cutoff frequency, a critical parameter, analyzing the characteristics of capacitance, resistance, and cutoff frequency of devices under different N-GaAs doping concentrations and layer thicknesses. The research is divided into two structural design approaches: varying doping concentration (with a fixed active layer thickness of 200 nm) and varying active layer thickness (with a fixed doping concentration of ).The findings indicate that, with a fixed N-GaAs layer thickness of 200 nm, the dynamic cutoff frequency increases initially with doping concentration, reaches a peak of 4.2 THz at an optimal doping concentration of , and then decreases. When the doping concentration increases from to , the dynamic cutoff frequency improves, primarily due to the increase in the capacitance modulation ratio as doping concentration rises. Additionally, the reduction in series resistance caused by higher doping concentration further enhances the cutoff frequency. However, when the doping concentration continues to increase, the capacitance modulation ratio saturates. At this point, the significant increase in zero-bias junction capacitance due to higher doping concentration dominates, resulting in a reduction in the dynamic cutoff frequency.In the layer thickness study, with a fixed doping concentration of, the optimal layer thickness is 340 nm, yielding a dynamic cutoff frequency of 4.5 THz. As the layer thickness increases from 100 nm to 340 nm, the rapid rise in the capacitance modulation ratio offsets the impact of the increased series resistance, leading to a significant improvement in the dynamic cutoff frequency. However, when the layer thickness exceeds 340 nm, the capacitance modulation ratio saturates, and the excessive thickness increases the series resistance, causing the dynamic cutoff frequency to decline.This study elucidates the dynamic cutoff frequency characteristics and provides optimal structural parameters for achieving high dynamic cutoff frequencies. The findings serve as a theoretical foundation and guide for future device design.