InP-based metamorphic InGaAs photodetector structures with lattice mismatch up to 2.6% were grown on InAlAs graded buffers with a relatively high mismatch grading rate of 1.1%μm-1 by gas source molecular beam epitaxy.They were compared to the samples with the same structures but smaller lattice mismatch of 1.7% and 2.1% to the InP substrate.Characteristics of the wafers were investigated by the measurements of atomic force microscopy,x-ray diffraction,photoluminescence and device performances.Results show that moderate surface morphology,large degree of relaxation and feasible optical characteristics have been obtained for the photodetector structures with lattice mismatch of 2.6%.The cut-off wavelength of the device is about 2.9μm at room temperature.The typical dark current of 2.56μA at room temperature has been achieved at reverse bias of 10 mV for the photodetector with 300 μm diameter.