Polarization-independent photodetector with ring-type grating

We propose a polarization-independent Au/Si Schottky-type photodetector with a ring-type grating that excites surface plasmon polaritons. The electromagnetic fields in ring-type and rectangular-type grating structures are calculated using the finite-difference time-domain method. For samples with the two geometries (slit width of 100 nm, slit pitch of 440 nm, and Au film thickness of 300 nm), the polarization dependence of the photocurrent is measured and compared. We confirm that the ring-type grating photodetector has a polarization-independent photocurrent, whereas the rectangular-type grating photodetector has only higher sensitivity at specific polarization angles.