Omnidirectional Near-Unity Absorption in an Ultrathin Planar Semiconductor Layer on a Metal Substrate

Abstract

We present omnidirectional near-unity absorption of light in an ultrathin planar semiconductor layer on a metal substrate. Using full-field simulations and a modal analysis, it is shown that more than 98% of the incident light energy can be absorbed in a mere 12 nm thick Ge layer on a Ag substrate at the wavelength of 625 nm over a wide range of angles (80% absorption up to 66° in the transverse magnetic and 67° in the transverse electric polarizations). The physical origin of such remarkable absorption properties is the coupling of incident light to the Brewster mode supported by the structure. The modal dispersion connects several critical coupling points in a dispersion diagram at which the absorption is unity and exhibits a virtually flat dispersion relation for both polarizations, resulting in omnidirectional, near-unity absorption. Potential applications of this simple, planar geometry such as photodetectors and solar cells made from various semiconductor materials are also discussed along with feasible charge-extracting structures and performance estimates.

New Insight into the Angle Insensitivity of Ultrathin Planar Optical Absorbers for Broadband Solar Energy Harvesting

“…attributed the omnidirectional behavior to the ultrathin feature in their optical absorbers and estimated that “as these coatings are much thinner than the wavelength of light, there is little phase accumulation due to the propagation through the film compared with the reflection phase change on reflection.” However, Lee et al 16. and Park et al 17. found that the angle insensitivity resulted from the specific relationship between the propagation phase in the lossy medium and the reflection phase change from the metal.…”

Perfect magnetic mirror and simple perfect absorber in the visible spectrum

“…We note that the studied structure is similar to the structure recently investigated experimentally in [20]. Here, in contrast to that work, we provide a thorough physical justification and a complete description of the mechanism through which nearly perfect absorption is possible, and complement the analysis with an experimental validation of an optimized absorber.…”

“…Here, in contrast to that work, we provide a thorough physical justification and a complete description of the mechanism through which nearly perfect absorption is possible, and complement the analysis with an experimental validation of an optimized absorber. We prove that it is possible to compensate admittances in a thin layer in a quasistatic way, and not through a wave interference as described in [20]. Finally, we analyze the material-parameter limitations for the frequency ranges where…”

Backside absorbing layer microscopy: Watching graphene chemistry

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