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We have fabricated a metal-semiconductor-metal Schottky photodetector on a semi-insulating InP substrate using a nominally lattice-matched In0.52Al0.48As/In0.53(GaxAl1−x)0.47As (graded)/In0.53Ga0.47As structure grown by molecular beam epitaxy. On average the graded quaternary layer enhanced the responsivity by about 35% compared to an identical device without the graded region, reaching a maximum of 0.45 A/W at 10 V applied bias. The associated dark current was 95 nA; the dark capacitance was 90 fF. High-speed measurements with a gain-switched 1.3 μm laser diode demonstrated an instrumentation-limited impulse response of 50 ps.

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