In this paper, we report on the fabrication a GaAs metal-semiconductor-metal photodetector with both low dark current and high responsivity at 850 nm. By using the Schottky contacts modified by a thin, n+-doped layer on the surface of the devices, the lowest dark current density of about 4.5 × 10-7 cm-2 was achieved. Besides, in the same devices, the responsivity resulting from a newly designed resonant-cavity-enhanced structure with a superlattice distributed Bragg reflector was about 0.34 A W-1 at 850 nm. The equivalent external quantum efficiency of the devices with equal finger spacing and finger width was about 48%. Our design is relatively easy and reproducible for both the sample growth and the device process.