Achieving higher photoabsorption than group III-V semiconductors in silicon using photon-trapping surface structures

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

The potential of pineapple leaf fibre as an acoustic absorber

This study discussed an alternative material known as pineapple leaf fibres (PALF) as a replacement of synthetic fibres in sound absorber production. The samples were fabricated from two different sizes of PALF, with and without binder of different thicknesses and densities to determine their effects on the sound absorption coefficient (SAC). The performance of SAC was measured by using an impedance tube instrument according to ISO 10534-2. The resulting frequency peak value of PALF obtained was in the range of 1–2 kHz. The results demonstrated PALF as a new hope for environmentally-friendly sound absorption material in replacing synthetic fibres. The PALF was capable of achieving SAC of more than 0.9 on average above 1 kHz by keeping the densities and thicknesses of the fibres under control. Additionally, the acoustic performance of PALF specimens was better than that of synthetic absorbers available in the market. Therefore, PALF is a promising natural fibre that can be potentially used as a sound absorber material