The material quality is very important to obtain 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 the InAs/InAsSbP system grown by LPE technology， there is an appropriate value for the lattice mismatch between InAsSbP and InAs. 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 6.8×10⁹ cm Hz^1/2W^-1 at zero bias， which is comparable with that of international commercial InAs photodetectors.