Abstract
We use finite-difference time-domain (FDTD) simulations to demonstrate enhanced infrared absorption in a photodetector covered with a microstructured metal film consisting of a metal-plasmon grating collector/ concentrator and sub-wavelength detector well; for circular gratings we use radial FDTD, and for linear gratings we use two-dimensional FDTD. We identify a figure of merit to quantify the improvement in signal-to-noise ratio of such a detector scheme. We optimize grating parameters for a circular grating surrounding a simple hole, showing that the signal-to-noise ratio can be improved by a factor of as much as 5.2, whereas the signal-to-noise improvement for comparable linear gratings is at most 1.7. In the case of the circular grating, this result is achieved with more than 400 times as much light absorbed in the hole as with a metal film but no grating.
Highlights
It has been established that the transmission of light through a hole in a metal film can be enhanced by microstructuring of the top surface of the film with a grating; the grating couples incident light to surface plasmon polaritons (SPPs), which are guided into the hole [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]
We use finite-difference time-domain (FDTD) simulations to demonstrate enhanced infrared absorption in a photodetector covered with a microstructured metal film consisting of a metal-plasmon grating collector/concentrator and sub-wavelength detector well; for circular gratings we use radial FDTD, and for linear gratings we use two-dimensional FDTD
We identify a figure of merit to quantify the improvement in signal-to-noise ratio of such a detector scheme
Summary
It has been established that the transmission of light through a hole (or a slit) in a metal film can be enhanced by microstructuring of the top surface of the film with a grating; the grating couples incident light to surface plasmon polaritons (SPPs), which are guided into the hole [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]. But related observations of this enhancement have been made at THz [16, 17] and microwave [18,19,20,21] frequencies This same phenomenon can enhance absorption in a dielectric material inside or beneath the hole [22, 23] or in similar geometries important for photodetection and photovoltaic applications [24, 25]. As we demonstrate below, enhanced absorption compared to a metal film with a hole and no grating is not a sufficient condition for achieving F > 1, and previously proposed detector designs do not achieve F > 1 [22, 23]. We optimize grating parameters to show that it is possible to increase the signal-to-noise ratio of a photodetector pixel using a metal grating
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