Introducing a blocking barrier with a wide bandgap can effectively lower the dark current of a traditional pn-junction infrared photodetector. The energy band diagrams of detectors are obtained by simulation using COMSOL software, and the simulation denotes that n- or p-type doping of the InAsSbP quaternary alloy sinks the valence band and lifts the conduction band in its energy map, thereby blocking holes or electrons. Through the theoretical analysis and simulation calculations, the compositions of InAsSbP necessary to satisfy the requirements of the blocking barrier are determined. The optimal values of the blocking-barrier thickness and doping concentration (particle-number concentration) are provided for the nBip and pBin infrared photodetectors by simulation, respectively. Further, the effects of the deviations from these optimal values on the dark currents of devices are analyzed. For the nBip detector, the maximum on-off ratio is obtained when the thickness and doping concentration are 40 nm and 2×10 18 cm -3, respectively, while for the pBin detector, the thickness and doping concentration are 60 nm and 4×10 17 cm -3, respectively.