Polarization-insensitive omnidirectional multiband absorption using metal-semiconductor multilayers

Abstract

The metal-dielectric (MD) multilayer structures have gained much interest in the area of optoelectronic and photonic devices, such as light emitting diodes (LEDs), photodetectors (PDs), optical filters, photovoltaic (PV) cells. In particular, an MDM structure, an ultra-thin dielectric slab surrounded by metal layers, has been of growing interest, because it can directly couple waveguide modes to free space modes, provided a metal layer is thin enough to allow the coupling. For light absorber applications, it is desired to possess polarization- and angle-insensitive resonances to maximize the efficiency. To achieve this performance, previous works require complex patterns on the top of the metal layer which cause significant fabrication challenges. To remove the need of having complex structures, the unpatterned metal-dielectric-metal (MDM) structure is proposed to effectively achieve polarization-insensitive omnidirectional multiband absorber in the visible and near-infrared light. To understand material dependent absorption characteristics, highly efficient light absorption properties in metal-semiconductor planar multilayers are studied. The present work numerically investigate the dispersion curves and the absorption spectra in a MDM structure based on the transfer matrix method (TMM). The multiband absorption based on the radiative waveguide modes (RWMs) can support strong light absorption and weak dependence on the angle of incident light and its polarization state. Multiple resonant-modes can maintain high absorptivity (> 0.9) and cross-polarization coupling (> 0.85) from normal incidence angle ($0^\circ$) to high grazing angle ($70^\circ$). The presented work is expected to provide a cost-effective solution to applications in optical sensing and optical communications.