High performance photodetectors operating in the 1.3 - 1.6 µm wavelength range are vital components for long-haul optical fiber communication systems. GaAs with its mature fabrication methods is one of the most used semiconductors in photodetector technology, but with a low cut-off wavelength around 870 nm. To use GaAs at longer wavelengths, a new growth technique has been developed, in which GaAs was grown at low temperatures (LT-GaAs), so that it absorbs photons with wavelengths up to 1.7 µm. In this work, we report the design, growth, fabrication, and characterization of GaAs-based high-speed p-i-n photodiodes operating at 1.55 µm. A LT-GaAs layer was used as the absorption layer and the photoresponse was selectively enhanced at 1.55 µm using a resonant cavity detector structure. The bottom mirror of the resonant cavity was formed by a highly reflective 15-pair GaAs/AlAs Bragg mirror. Molecular beam epitaxy was used for wafer growth, where the active LT-GaAs layer was grown at a substrate temperature of 200 °C. The fabricated devices exhibited resonance around 1548 nm. When compared to the efficiency of a conventional single-pass detector, an enhancement factor of 7.5 was achieved. Temporal pulse-response measurements were carried out at 1.55 µm. Fast pulse responses with 30 ps pulse-width and a corresponding 3-dB bandwidth of 11.2 GHz was measured.