Investigation Of Broandband Absorption In Transition Metal Dichalcogenides Based Structures

In recent years,monolayer graphene has attracted wide interest due to its unique electro-optical properties.However,the zero band gap of monolayer graphene limits its further applications in optoelectronic devices.The emergence of transition metal dichalcogenides has overcome this shortcoming and opened up new research directions in the fields of electronics and optoelectronics.As a representative of transition metal dichalcogenides,monolayer molybdenum disulfide(MoS₂)is a direct band gap semiconductor,which is the promising candidate for manufacturing the flexible phototransistors,photodetectors and solar cells.Based on the transmission matrix method and the rigorous coupled wave analysis method,we systematically study the optical absorption of several structures containing monolayer MoS₂ and achieve high broadband optical absorption in the visible light range.The main research work of this paper is as follows:Firstly,the optical absorption of one-dimensional Octonacci quasi-periodic photonic crystal composed of monolayer MoS₂,Si and SiO₂ has been studied.It is found that the high optical absorption can be achieved in a wide wavelength range by optimizing the thicknesses of the components and the period number of the quasi-periodic structure for different Octonacci orders.In addition,the shape,position and range of the high optical absorption can be adjusted by the incident angle or the polarized state of the incident wave.Our results show that the quasi-periodic photonic crystal enables a new chance to achieve the broadband and high optical absorption of monolayer transition metal dichalcogenides without the presence of the metal.Secondly,the optical absorption of the one-dimensional Thue-Morse quasi-periodic photonic crystal composed of monolayer MoS₂,non-metallic Si₃N₄ and SiO₂ has been discussed.We find that the high optical absorption exceeding 90%can be obtained in a wide frequency range for Thue-Morse quasi-periodic photonic crystals with the different sequences by optimizing the thicknesses of the components and the number of periodic repetitions of the quasi-periodic structure.When the Thue-Morse quasi-periodic photonic crystal with a sequence number of four can achieve nearly 100%optical absorption in the wavelength range of 579 nm-617 nm under normal incidence.In addition,we have also discussed the influence of incident angle on the absorption characteristics of Thue-Morse quasi-periodic photonic crystal structure with the different sequences.Our work confirms that the Thue-Morse quasi-periodic photonic crystal can also improve the optical absorption properties of monolayer transition metal dichalcogenides.Finally,the optical absorption of the hybrid structure with the Thue-Morse quasi-periodic photonic crystal consisting of monolayer MoS₂,SiO₂ and Si₃N₄ and the metal Ag grating structure has been investigated.It is found that the combination of the two above structures can effectively improve the optical absorption value of the hybrid structure in the entire wavelength range under the TM and TE polarized incident lights.In addition,the number of grooves in Ag grating structure has a significant influence on the optical absorption of the hybrid structure.In particular,the hybrid structure can achieve a high optical absorption more than 80%in the range of 300 nm-465 nm in the case of a single groove and it can reach the even higher optical absorption value(more than 90%)in the wavelength range of 550 nm-635 nm for three grooves.Our results provide new possibilities for further expanding the high optical absorption of monolayer transition metal dichalcogenides.