Near-infrared
(NIR) photodetectors are crucial to various
applications,
including face recognition, night vision, and laser detection and
ranging (LiDAR). However, conventional silicon (Si)-based photodetectors
exhibit poor sensitivity in the NIR region (λ = 750–1060
nm) because of low photoabsorption within the photoabsorption layer.
To overcome this limitation, we proposed a plasmonic diffraction approach
that can improve photosensitivity in the NIR regime by properly designing
the period of the metal nanograting required to diffract the incident
light at large angles in Si, thereby extending the effective propagation
length in the photoabsorption layer. In addition, the metal nanograting
can transmit the specific wavelength and polarization while enhancing
photosensitivity through optimized geometric design. It can be highly
advantageous for active sensing applications such as LiDAR, which
offers the distinction between signal and noise by selectively transmitting
specific wavelengths and polarizations. However, the effectiveness
of plasmonic diffraction has never been experimentally demonstrated
because it requires the fabrication of a metal nanograting structure
with a fine gap. In this study, we successfully fabricated a gold
nanograting array on a photodetector and demonstrated a significant
improvement (1.79×) in its photosensitivity while employing it
as a bandpass filter as well as a polarization filter, even with a
single thin gold layer. In addition, providing highly reflective trenches
at the border of each pixel will allow the diffracted light to be
confined within the pixel, leading to the expansion of image sensors
while increasing photosensitivity. This breakthrough will usher in
further advances in nanophotonic devices that will enable the development
of active sensing technologies with high signal-to-noise ratios.