In this paper, diffractive microlens arrays are studied to concentrate incident light onto the effective photosensitive area of InSb infrared focal-plane arrays and thus enhance the quantum efficiency and reduce the crosstalk. Four designs of diffractive microlenses are investigated by a phase-matched Fresnel-elements approach. The quantum efficiency and crosstalk of the devices are calculated by using a two-dimensional device simulation with unit cell of 50 μm. Light propagation through the diffractive microlenses is simulated by the finite-difference time-domain method based on a rigorous vector solution of Maxwell's equations. The results show that the highest quantum efficiency of the device with a diffractive microlens array is about 51.6% and the corresponding crosstalk is 5.06%. The quantum efficiency is 2.1% higher than that of the device with a spherical refractive microlens array. © 2014 TMS.