  Surface plasmon resonance (SPR) has been widely utilized to improve the
absorption performance in the photosensors. Graphene has emerged as a promising
plasmonic material, which supports tunable SPR and shows significant
flexibility over metals. In this letter, a hybrid photosensor based on the
integration of periodic cross-shaped graphene arrays with an ultrathin
light-absorbing semiconductor is proposed. A tenfold absorption enhancement
over a large range of the incidence angle for both light polarizations as well
as a considerably high photogeneration rate ($\sim10^{37}$) is demonstrated at
the resonance. Compared with traditional metal-based plasmon-enhanced
photosensors, the absorption enhancement here can be expediently tuned with
manipulating the Fermi energy of graphene. The proposed photosensor can amplify
the photoresponse to the incidence light at the selected wavelength and thus be
utilized in photosensing with high efficiency and tunable spectral selectivity
in the mid-infrared (mid-IR) and terahertz (THz) regime.
