GaAs based wavelength extending metamorphic In0.83Ga0.17As photodetector structures with cut-off wavelength around 2.5 mu m and lattice mismatch up to 5.9% were grown by gas source molecular beam epitaxy. In this structure, continuously composition graded InxAl1-xAs was used as buffer layer. Compared to the InP-based photodetector with similar structure, the GaAs-based In0.83Ga0.17As photodetector structure shows almost the same degree of relaxation and a little larger residual strain, but lower lattice quality and poorer surface morphology, as well as relatively weaker photoluminescence intensity probably due to more non-radiative recombination centers formed in the In0.83Ga0.17As epilayer For the photodetectors with 200 pm mesa diameter, the typical dark currents (V-R=10 mV) are 819 nA and 159 nA at 300 K for GaAs-based and InP-based In0.83Ga0.17As PDs, respectively, which leaves room for optimization of the structure. (C) 2013 Elsevier B.V. All rights reserved