The function of rapid thermal annealing on zinc-diffused In_0.53Ga_0.47As/InP PIN detector was systemically studied. By using electrochemical capacitance-voltage and secondary ion mass spectroscopy techniques， Zn and net acceptor concentration profiles were investigated， indicating that the annealing process would affect the dopant concentration but not affect the diffusion depth. In_0.53Ga_0.47As/InP PIN detectors under different annealing conditions were fabricated， the results showed that the detector without annealing process outperformed in terms of lower device capacitance and higher activation energy from 260 to 300K. By analyzing the mechanism of dark current， the unannealed sample exhibited lower Shockley-Read-Hall generation-recombination and diffusion currents， explaining the higher peak detectivity at room temperature. Therefore， for the purpose of fabricating high-performance planar InGaAs detectors with low-doped absorption layer， annealing process is inadvisable.