The optical absorption of graphene layers prepared on top of a one-dimensional photonic crystal (1DPC) is investigated theoretically. The absorption of graphene with 1DPC is enhanced greatly over a broad spectral range due to photon localization. The absorption of graphene can also be tuned by varying either the incident angle or the distance between the graphene and the 1DPC. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4740261]NSFC [10904059, 10904016, 11104232]; NSF from the Jiangxi Province [2009GQW0017]; Fujian Innovation Fund [2009J05006

By extracting the permittivity of monolayer MoS 2 from experiments, the optical absorption of monolayer MoS 2 prepared on top of one-dimensional photonic crystal (1DPC) or metal films is investigated theoretically. The 1DPC and metal films act as resonant back reflectors that can enhance absorption of monolayer MoS 2 substantially over a broad spectral range due to the Fabry-Perot cavity effect. The absorption of monolayer MoS 2 can also be tuned by varying either the distance between the monolayer MoS 2 and the back reflector or the thickness of the cover layers. c 2016 Optical Society of America Monolayer MoS 2 as a new kind of two dimensional (2D) semiconductor has elicited significant attention because of its distinctive electronic and optical properties [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Monolayer MoS 2 exhibits a direct band gap in the visible frequency range [1][2][3][4], which is more favorable for optoelectronic applications than graphene in numerous cases. Monolayer MoS 2 has show numerous potential applications in flexible phototransistors, photodetectors, photovoltaics, and signal amplification [5][6][7][8][9][10][11][12][13]. Notably, the photoresponsivity of monolayer MoS 2 photodetectors can reach 880 A/W, which is 10 6 better than that of the first graphene photodetectors (∼0.5 mA/W) [5]. The optical absorbance in monolayer MoS 2 is minimal (< 11%) due to its ultrathin thickness, which is not conducive to fabrication of photodetectors, solar cells, and optical amplification. Thus, to promote the applications of monolayer MoS 2 , the optical absorptance in monolayer MoS 2 waves should be enhanced. In studies of graphene, several mechanisms have been proposed to enhance the absorption of graphene, e.g., periodically patterned graphene, surface plasmon, microcavity, graphene-negative permittivity metamaterials, and attenuated total reflectance, etc [15][16][17][18][19][20][21][22][23]. The interaction between graphene and optical beams can also be enhanced when the graphene layers are prepared on top of one-dimensional photonic crystal (1DPC) or with resonant metal back reflectors because of the Fabry-Perot (F-P) cavity effect [24][25][26]. The proposed structures are very easy to fabricate using existing technology.In this Letter, the optical absorption of monolayer MoS 2 prepared on top of 1DPC or metal films with a spacer layer and cover layers is investigated theoretically. We find that the absorption of monolayer MoS 2 can be enhanced by nearly four times because of the F-P interference. The absorption of monolayer MoS 2 with 1DPC is slight larger than that of monolayer MoS 2 with metal films. However, the full width at half maximum (FWHM) of the absorption spectrum of monolayer MoS 2 with metal films is much larger than that of monolayer MoS 2 on top of 1DPC. The absorption of monolayer MoS 2 can also be tuned by varying the thickness of spacer layers and cover lay-1

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We investigate THz absorption properties of graphene-based heterostructures by using characteristics matrix method based on conductivity. We demonstrate that the proposed structure can lead to perfect THz absorption because of strong photon localization in the defect layer of the heterostructure. The THz absorption may be tuned continuously from 0 to 100% by controlling the chemical potential through a gate voltage. By adjusting the incident angle or the period number of the two PCs with respect to the graphene layer, one can tailor the maximum THz absorption value. The position of the THz absorption peaks can be tuned by changing either the center wavelength or the thicknesses ratio of the layers constituting the heterostructure. Our proposal may have potentially important applications in optoelectronic devices.