(Invited) Broadband and Broad Angle Enhanced Light Absorption in MoS2 based Hetero Plasmonic Structure
Authors: Imam Safayat Al , Ishtiak Khandakar Mohammad , Khosru Quazi Deen Mohd 
Published: November 2022

Solar cells, photovoltaic devices and optoelectronic elements needs enhanced light absorption with a wide range of incident angle for better and efficient design. Two-dimensional (2D) materials have exceled in all areas including electrical applications, optical modulations, mechanical as well as chemical implementations due to their direct bandgap and high optical absorption nature[1]. Photon irradiation allows to generate electron-hole pairs in a direct bandgap material such as TMDCs which makes them potential candidates for large amount of light to be trapped. Different structures have been studied to achieve high optical absorption [2][3]. Although one dimensional photonic crystal(1DPC) and defective PC has good optical absorption with wide range and angle [4],[2] number of layers and complexity in structure has made it difficult to be fabricated. MoS2 monolayer structure based on cover spacer, plasmonic and dual substrate layer (SiO2(50nm)/Si ) has also increased optical absorption range and broad angle [5] but TMDC based heterostructures with spacer has improved absorption comparing to previous structures without metallic layer [6]. In this paper, we proposed a dual TMDC-spacer based plasmonic structure with dual substrate for wide and broad range and angle of near perfect optical absorption.

The structure considered here is an air/MoS2/Spacer1/MoS2/Spacer2/plasmonic/dual substrate with 0.665nm, 70nm and 50nm layer of MoS2, Au as plasmonic layer and SiO2 as part of dual layer with Si as lossless substate. (Figure 1) For spacers SiO2 and TiO2 are taken with optimized value (figure 2) of 92 and 68nm for enhanced absorption. The transfer matrix of the constituted layer for either transverse electric (TE) or transverse magnetic (TM) polarization was determined using the transfer matrix method (TMM). Both in TE and TM mode, the ~30 and ~40% of enhanced light absorption are observed in proposed structure compared to hetero and mono layer structure (figure 3) with impact of metallic and spacer layer. In case of incident angle, both at resonance frequency of MoS2 and within visible range, broad angle range (00-400 for TE and 00-800 for TM) is observed with wider wavelength. (Figure 4 and figure 5). Impact of various metallic layer on the proposed structure is also observed (Figure 6). Structure with VO2 as plasmonic layer [7] has around ~95% of peak absorption (400nm-550nm) and wide incident angle (00-850) irrespective of polarizations with lieu of spacer hetero-TMDC-stack (Figure 7). Due to multiple layers of structures, collective surface plasmon polaritons (SPP) has an enhanced light absorption within the heterostructure and enhanced electric field distribution of the structure is observed (Figure 8).

Table I lists some comparison among various structures and parameters indicates that proposed dual spacer -TMDC based plasmonic heterostructure has wide visible range of wavelength (400-550 nm) with broad angle (00-850) light absorption with both polarizations compare to other counterparts.

In this work an enhanced range in both wavelength and incident angle of visible optical absorption is observed in both polarization with plasmonic dual heterostructure is observed and compared with other structures. Such structures are useful for photodetectors and solar cells for maximum absorptions.

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Figure 1