The design and fabrication of a InP/InGaAs modified uni-traveling carrier photodetector array heterogeneously integrated on the thin-film lithium niobate platform was proposed and fabricated. The 1×N multimode interferometers were employed to ensure uniform distribution of input optical power to each photodetector unit. Experimental results demonstrate that the 1×2, 1×3, and 1×4 photodetector arrays achieve 3 dB bandwidths of 50 GHz, 45 GHz, and 40 GHz, respectively. The device was applied in an intensity modulation direct detection system, successfully achieving high-quality reception of 60 Gbaud and 100 Gbaud four-level pulse amplitude modulation signals.