The material quality is very important for obtaining the high performance infrared detector. It is presented that the key issue of the material quality is to control the lattice mismatch between the layers of the device architecture. The effects of the lattice mismatch on the material quality and the dark current characteristics were reported. In InAs/InAsSbP system grown by LPE technology, the lattice mismatch between InAsSbP and InAs is not the smaller the better, but has an appropriate value. If the lattice mismatch deviates from this value, no matter whether it is smaller or larger, the material quality will deteriorate. Then it was stated how to adjust growth parameters to obtain the appropriate lattice mismatch. The infrared detector made from the device architecture with the appropriate lattice mismatch was fabricated, and the room-temperature peak detectivity of this detector is 6.8×109cm Hz1/2W-1 at zero bias, which is comparable with that of international commercial InAs photodetectors.