We demonstrate that high-quality lattice-mismatched In0.73Ga0.27As:InP photodetectors for use at 2.2 μm can be grown by molecular beam epitaxy using compositionally graded buffer layers. By investigating various growth conditions, we found that the quality of the active layer material depends on the thickness of the compositionally graded buffer layers and the substrate temperature during the growth of the compositionally graded buffer layers and active layers. The best device performance was obtained from a sample with a 1.0 μm compositionally graded buffer grown at a substrate temperature of 350 °C combined with active layers grown at 400 °C. The typical room temperature dark current at a reverse bias of 1 V for 100×100 μm2 photodetectors on this sample was 2 mA/cm2. This dark current is a factor of 10 better than that of commercially available devices fabricated from material grown using vapor phase epitaxy. © 1997 American Vacuum Society.