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Metamorphic In/sub 0.53/Ga/sub 0.47/As p-i-n photodiodes on GaAs substrate exhibiting the lowest dark current ever reported were fabricated and characterized. Their dark current, DC and RF performances were measured and compared for devices of different sizes. Typical dark current for 15-μm-diameter devices was 600 pA under 5-V reverse bias, corresponding to a dark current density of 3.40×10/sup -4/ A/cm2. Typical responsivity measured with 1.55-μm optical radiation was 0.55 A/W corresponding to an external quantum efficiency of 44%. The electrical 3 dB bandwidths of the photodiodes with diameters smaller than 20 μm were over 20 GHz.