High-performance thin-film epitaxial lift-off (ELO) photodetectors have potential for integration with independently optimized integrated circuits and waveguides. In this paper, the dark current, responsivity, and frequency response of GaAs/AlGaAs metal-semiconductor-metal (MSM) photodetectors that remain on the growth substrate are compared to ELO detectors with and without back passivation. The passivated ELO detectors perform comparably to the on-wafer devices, while the unpassivated devices exhibit performance degradation. In addition to demonstrating the importance of back passivation, this paper presents the lowest ELO MSM dark current (5 nA at 5 V) for a 200-μm-diameter device published to date.