High-speed and high-efficiency photodiodes are especially beneficial for exponential data communication traffic growth. However, improving high responsivity while maintaining low dark current and high bandwidth remains a challenge for vertical detector design. This study proposes a plasmonic InP/InGaAs uni-traveling-carrier photodiode with optical antenna arrays, which exhibits a low dark current of 2.52 nA at a −3 V bias voltage, a high bandwidth of over 40 GHz, and a high responsivity of 0.12 A/W. The absorption efficiency of the photodiode shows 2-fold improvement using plasmonic resonance generated by nanodisks at 1550 nm. This work designs a low dark current and high-bandwidth photodiode with improved responsivity, which provides a potential method for high-speed vertical photodiode design.