The effects of thickness and period number of In0.6Ga0.4As/InAs superlattice electron barrier on the performances of InP-based metamorphic In0.74Ga0.26As detectors have been investigated. The samples were grown by molecular beam epitaxy and characterized by high resolution X-ray diffraction reciprocal space maps, photoluminescence, atomic force microscope, plan view transmission electron microscopy and the device dark current measurements. Results show that the dark currents are reduced by insertion of an electron barrier with moderate thickness and period number in the absorption layer, but a superlattice electron barrier structure with excessive thickness and period number can lead to the deterioration of the material quality and device performances.