All-Silicon Ultra-Broadband Infrared Light Absorbers

Abstract

Absorbing infrared radiation efficiently is important for critical applications such as thermal imaging and infrared spectroscopy. Common infrared absorbing materials are not standard in Si VLSI technology. We demonstrate ultra-broadband mid-infrared absorbers based purely on silicon. Broadband absorption is achieved by the combined effects of free carrier absorption, and vibrational and plasmonic absorption resonances. The absorbers, consisting of periodically arranged silicon gratings, can be fabricated using standard optical lithography and deep reactive ion etching techniques, allowing for cost-effective and wafer-scale fabrication of micro-structures. Absorption wavebands in excess of 15 micrometers (5–20 μm) are demonstrated with more than 90% average absorptivity. The structures also exhibit broadband absorption performance even at large angles of incidence (θ = 50°), and independent of polarization.

Engineering Light at the Nanoscale: Structural Color Filters and Broadband Perfect Absorbers

“…The absorption around this resonance gets significantly broadened due to the high loss of Ti, which lowers the Q‐factor of the waveguide cavity. To date, other refractory metals as Ti have also been demonstrated for broadband absorption and semiconductors such as silicon (Si) and germanium (Ge) can be included instead of transparent insulators for extra absorption improvement . Interestingly, an additional propagating surface plasmon resonance (PSPR) excited at the short wavelength (Figure d,g,i) due to the relatively large Ti pattern period further boosted the absorption as presented by the other absorption peak at 914 nm in Figure b.…”

Quad-Band Plasmonic Perfect Absorber for Visible Light with a Patchwork of Silicon Nanorod Resonators

“…In recent years, the silicon nanostructure has drawn increasing attention due to its ability to support plasmon resonance in the optical regime [ 29 , 30 , 31 , 32 , 33 , 34 ]. Silicon is one of feasible high refractive index materials that has been widely used to design optical devices, such as solar cells [ 29 ], detectors [ 30 ], color filters [ 31 , 32 ], photonic waveguides [ 33 ], and absorbers [ 34 ]. It has been demonstrated that this plasmon resonance in the silicon nanostructure could be tuned to enhance light absorption in the infrared and visible ranges [ 34 , 35 , 36 , 37 ].…”

“…Silicon is one of feasible high refractive index materials that has been widely used to design optical devices, such as solar cells [ 29 ], detectors [ 30 ], color filters [ 31 , 32 ], photonic waveguides [ 33 ], and absorbers [ 34 ]. It has been demonstrated that this plasmon resonance in the silicon nanostructure could be tuned to enhance light absorption in the infrared and visible ranges [ 34 , 35 , 36 , 37 ]. The silicon-based PPA is easy to integrate into mature compatible complementary metal-oxide-semiconductor (CMOS) technology [ 34 ].…”

“…It has been demonstrated that this plasmon resonance in the silicon nanostructure could be tuned to enhance light absorption in the infrared and visible ranges [ 34 , 35 , 36 , 37 ]. The silicon-based PPA is easy to integrate into mature compatible complementary metal-oxide-semiconductor (CMOS) technology [ 34 ]. What is more, the scattered light from the silicon nanostructure can be promoted to generate LSPR by exciting the free electrons of the plasmonic gold material.…”

“…What is more, the scattered light from the silicon nanostructure can be promoted to generate LSPR by exciting the free electrons of the plasmonic gold material. For example, Kazim et al proposed a silicon based PPA for ultra-broadband absorption in the mid-infrared region, which can be fabricated using standard optical lithography [ 34 ]. Then, Liu proposed a PPA based on cavity mode using silicon patches array, multiband perfect absorption could be obtained in the infrared region [ 35 ].…”