Enhanced absorption of monolayer MoS2 with resonant back reflector

Abstract

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

Limits to the Optical Response of Graphene and Two-Dimensional Materials

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Active Control of Plasmon–Exciton Coupling in MoS2–Ag Hybrid Nanostructures

“… is the experimental MoS 2 dielectric response42 , f is the equivalent oscillator strength,  (118 meV) and   eVare the bandwidth and transition energy of the MoS 2 exciton. Oscillator strength f is direct proportional to the density of excitons which depends on the laser power P and corresponding absorption cross section A, as  f A P .…”

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