Research On The Optical Absorption Characteristics Based On Molybdenum Disulfide-grating Composite Structure

Transition-metal dichalcogenides（TMDs）including MoS₂,WS₂,WSe₂,and MoSe₂has demonstrated many unique electronic and optical properties,such as direct band gaps,ultra-high conductivity and atomic-sized thickness,attracting the significant attentions in advanced optoelectronics and electric devices.The light absorption in free-standing monolayers of TMDs is only about 10-20%.Development of the TMDs-based resonance structure with high light absorption capability hold the potential in applications of solar cell,photodetector and biosensor.In this dissertation,we have systemically investigated the absorption characteristics of three types of MoS₂-grating resonant structures.Structures for single-or multi-channel absorption has been designed over visible spectrum based on different physical mechanisms.The main contents of this thesis are listed below:（1）We have systemically investigated the optical characteristics of molybdenum disulfide.The research works related to the MoS₂-based resonant structures has been summarized.In addition,the basic numerical computation methods used in this thesis has been introduced.（2）We have designed a novel structure of molybdenum disulfide coupled to a periodic silver nano-groove array with a silica spacer to achieve a perfect absorber in the visible region.Due to the high extinction coefficients of molybdenum disulfide,a near-unity absorber is achieved in the visible region by utilizing the original magnetic resonance in the nanogroove.Simulated results are in excellent agreement with theoretical analysis.The small changes in the structural parameters of nanogrooves give rise to the advantageous tunability of the wavelength of the absorption peak.The high absorption of light in MoS₂ remains unchanged over a wide angular range of incidence.Meanwhile,the high enhancement of absorption in other TMDs can be achieved by using the same nano-groove array.These findings will open up new possibility for improving the light-matter interaction in the burgeoning two-dimensional layered materials and heterostructures,enhancing the absorption of TMDs-based photoluminescence and photodetection.（3）We have proposed a simply structure composed of a monolayer of MoS₂,a dielectric grating,a spacer,and a perfect electrical conductor（PEC）at visible spectrum.It has been demonstrated that the dual-band total absorption is enabled by the guided mode resonances with the critical coupling.MoS₂ has absorbed the full energy as the only lossy material in our proposed structure,achieve dual tunable total absorption.Intriguingly,by choosing the proper structural parameters,the resonance wavelength can be controlled with a small change,thus we can achieve a wavelength-selective spectrum.Meanwhile,we can achieve a dual channel or third channel photonics device by varying the incident angles.This work may hold a great potential for enhanced light-MoS₂ interaction,based-MoS₂ optoelectronic devices and multichannel modulators.（4）We have demonstrated a resonant perfect absorption with a ultra-narrow linewidth through a periodic rectangle dielectric-dimer arranged in a square lattice on a gold mirror.Q-factor of the resonant perfect absorption can reach more than 1900.It has been shown that the perfect absorption is associated with the diffraction based critical coupling.Moreover,our simulated results indicate that the resonance wavelength can be tuned by the structural parameters and exhibits extremely high sensitivity to the refractive index of ambient medium as 675nm/RIU.Furthermore,we show this highly confined resonant mode can effectively enhance the absorption of two-dimensional（2D）materials covered on the top,such as graphene and MoS₂.The strong localized electric field and the resonance wavelength with high quality factor are beneficial for optical filters,detectors and surface enhanced Raman scattering in micro/nano-photonics.