The photoresponse ofIn0.5Ga0.5Asmetal–semiconductor–metal photodetectors is related to the presence of a hole trap. Detectors made from material grown with anIn0.5Al0.5Asbuffer layer had no measurable trap density when examined using deep-level transient spectroscopy, and the full width half maximum (FWHM) of the photoresponse was 80 ps at 5 V bias for 3 μm interdigitated fingers and spacings. Detectors made from material grown without anIn0.5Al0.5Asbuffer layer had a hole trap and a FWHM photoresponse of 220 ps. This deep hole trap is likely related to impurities that diffused upward from an interface of an InP substrate and an InGaAs epilayer.