The photosensitivity of silicon is inherently very low in the visible
electromagnetic spectrum, and it drops rapidly beyond 800 nm in near-infrared
wavelengths. Herein, we have experimentally demonstrated a technique utilizing
photon-trapping surface structures to show a prodigious improvement of
photoabsorption in one-micrometer-thin silicon, surpassing the inherent
absorption efficiency of gallium arsenide for a broad spectrum. The
photon-trapping structures allow the bending of normally incident light by
almost ninety degrees to transform into laterally propagating modes along the
silicon plane. Consequently, the propagation length of light increases,
contributing to more than an order of magnitude improvement in absorption
efficiency in photodetectors. This high absorption phenomenon is explained by
FDTD analysis, where we show an enhanced photon density of states while
substantially reducing the optical group velocity of light compared to silicon
without photon-trapping structures, leading to significantly enhanced
light-matter interactions. Our simulations also predict an enhanced absorption
efficiency of photodetectors designed using 30 and 100-nanometer silicon thin
films that are compatible with CMOS electronics. Despite a very thin absorption
layer, such photon-trapping structures can enable high-efficiency and
high-speed photodetectors needed in ultra-fast computer networks, data
communication, and imaging systems with the potential to revolutionize on-chip
logic and optoelectronic integration.Comment: 24 pages, 4 figure