▎ 摘　　要

In this paper, the performance of a graphene photodetector is investigated theoretically in the infrared spectral region (8-12 mu m). To increase the absorption of infrared radiation in the graphene layer, plasmon-polaritons are excited in the graphene layer by using dielectric grating. Due to the large propagation constants of plasmon-polaritons compared to the propagation constants of the electromagnetic waves in free space, the dielectric grating is required to provide the phase matching condition of plasmon-polaritons excitation. The results show that due to the excitation of plasmon-polaritons in the graphene layer, the infrared wave has been confined to a small reign around the graphene layer with a full width at half maximum (FWHM) of about 8 nm. Increasing in Fermi energy level leads to a shift in the wavelength of the infrared radiation required to excite plasmon-polaritons in the graphene layer towards shorter wavelengths, so that for the Fermi energy levels of 10, 30, 45, and 60 meV the required wavelengths for plasmon-polaritons excitation are 11.6, 10.6, 9.4, and 8.2 mu m, respectively. Under the incidence of the infrared radiation with these wavelengths, and at the corresponding Fermi energy levels, the responsivities of the photodetector at peak points are 2.74, 2.39, 2.19, and 2.04 mA/W, respectively. Therefore, this photodetector is tunable where the detection wavelength is changed by tuning the Fermi energy level of the photodetector. In addition, the results indicate that excitation of plasmon-polaritons approximately increases the responsivity by two times compared to the case without the plasmon-polaritons excitation.