  A general metallic mirror (i.e., a flat metallic surface) has been a popular
optical component that can contribute broadband light absorption to thin-film
optoelectronic devices; nonetheless, such electric mirror with a reversal of
reflection phase inevitably causes the problem of minimized electric field near
at the mirror surface (maximized electric field at one quarter of wavelength
from mirror). This problem becomes more elucidated, when the
deep-subwavelength-scaled two-dimensional (2D) material (e.g., graphene and
molybdenum disulfide) is implemented into optoelectronic device as an active
channel layer. The purpose of this work was to conceive the idea for using a
charge storage layer (spherical Au nanoparticles (AuNPs), embedded into
dielectric matrix) of the floating-gate graphene photodetector as a magnetic
mirror, which allows the device to harness the increase in broadband light
absorption. In particular, we systematically examined whether the versatile
assembly of spherical AuNP monolayer within a dielectric matrix (i.e., optical
metamaterial mirror), which should be designed to be placed right below the
graphene channel layer for floating-gate device, can be indeed treated as the
effective magnetic mirror. In addition to being capable of the enhancement of
broadband light absorption, versatile access to various structural motifs of
AuNPs benefitting from recent advances in chemical synthesis promises
compelling opportunities for sophisticated engineering of optical metamaterial
mirror. High amenability of the AuNP assembly with the semiconductor-related
procedures may make this strategy widely applicable to various thin film
optoelectronic devices. Our study thereby illustrates advantages in advancing
the design of mirror for rational engineering of light-matter interaction
within deep-subwavelength-scaled optoelectronic devices.
