Abstract
We present a theoretical feasibility study of the use of reflection grating couplers in order to harness the Surface Plasmon Polariton (SPP) to increase the absorption efficiency in the short wavelength infrared (SWIR) spectral range of a novel SWIR to visible (VIS) direct up-conversion imaging device. This device detects the SWIR spectral band photons using high absorption PbSe/CdSe core-shell, PbS nano-spheres or PbSe nano-columns. In order to further enhance the absorption of the SWIR light within the nano-structure layer we propose to add another light absorption enhancement, known as SPP enhanced absorption. The idea is to cover the absorber layer surface with a structured metal layer that will ignite SPPs on the metal – dielectric interface, by coupling between the incident TM polarized photons and the SPP modes; this results in better field confinement at the interface that will further increase the SWIR absorption of this thin layer. Calculation of the field profile of the surface plasmon (SP) in the SWIR range shows perpendicular dominance of the SP’s electrical field direction on the dielectric layer side (the PbS or PbSe/CdSe absorption layer side). Based on this result, it was found that, due to the use of quantum confined and, thus, high oscillator strength nanostructures, there is only a marginal increase in the absorption and, hence, in the quantum efficiency when using the SPP enhancement technique. Nevertheless, we show that one of the proposed configurations of the metal grating coupler, having a lamellar structure with a pitch of 1.38μm, a duty cycle (DC) of 0.12μm and a height of 60nm, is predicted to increase the total layer’s absorption by 9.5%, mainly due to efficient light scattering rather than to SPP enhanced absorption.
Highlights
Where the High Oscillator Strength (HOS) comes from the large Bohr radius of the PbSe/CdSe nano-spheres or nano-columns
The HOS of the large Bohr radius nano-structured materials presents much higher absorption compared to bulk materials; one can achieve sufficient absorption enhancement despite using a thin layer.[2]
This layer is covered with pixelated metal having a grating that ignites the Surface Plasmon Polariton (SPP) at the interface, where the generated photo holes drift, due to the external bias, to an organic light emitting diode (OLED) and recombine with the injected electrons; VIS light is emitted that is spatially correlated to the short wavelength infrared (SWIR) photons
Summary
Where the HOS comes from the large Bohr radius of the PbSe/CdSe nano-spheres or nano-columns. The HOS of the large Bohr radius nano-structured materials presents much higher absorption compared to bulk materials (such as InGaAs used for SWIR light absorption); one can achieve sufficient absorption enhancement despite using a thin layer.[2] Combining these HOS materials with the right SPP gratings, a very high absorption configuration can be achieved. Core-shell nano-spheres or nano-particles (NPs) of PbSe/CdSe, where the particle diameter determines its energy bandgap and, its absorption spectral band (1.3μm - 1.8μm) Such core-shell configurations feature a low electron-hole (e-h) recombination rate; due to high charge delocalization over the entire core-shell structure (e-h wave functions have low overlap). Since the device is positioned in close proximity to the eyes, such collimating optics is required
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