In last years, the introduction of new materials such as graphene has led to advances in the performances of silicon-based photonic devices. Here, we present an innovative type of photodetector based on graphene embedded between hydrogenated amorphous and crystalline silicon. More in detail, with the aim to increase the graphene optical absorption in the near-infrared spectrum, a photodetector based on low-finesse Fabry-Pérot optical microcavity has been investigated demonstrating responsivities of 26 mA/W around 1550nm. Furthermore, a photodetector integrated into a hybrid waveguide able to absorb the full incoming radiation has been numerically studied.