InP-based high indium content In0.83Ga0.17As photodetector structures with lattice mismatch up to 2.1% have been grown by gas source molecular beam epitaxy system. The photodetectors using continuously graded and step-graded InxAl1-xAs buffer structures were grown and demonstrated. The effects of the buffer scheme were investigated by the measurements of atomic force microscopy, high-resolution X-ray diffraction, photoluminescence and device performance. Results show that the full relaxation of the photodetector structure has been achieved by using continuously graded InAlAs buffer. Superior optical properties and lower dark currents can be reached for the photodetector structure with continuously graded buffer layer. (C) 2015 Elsevier B.V. All rights reserved.