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.
Highlights
By exploiting plasmonic structures, electromagnetic energy can be localized into a very small volume and efficient conversion between photons and plasmons can be controlled at sub-wavelength scale[1,2]
We show that the absorption is related to the free carrier absorption, and vibrational and plasmonic resonances supported by the structure simultaneously
Conventional optical lithography and deep reactive ion etching (DRIE) techniques are used for the microfabrication of the structures
Summary
Electromagnetic energy can be localized into a very small volume and efficient conversion between photons and plasmons can be controlled at sub-wavelength scale[1,2] Noble metals such as gold and silver are commonly used plasmonic materials at visible (VIS) and near-infrared (NIR) ranges. The performance of various semiconductor materials has been evaluated in a number of theoretical and experimental studies[5,6,7,8] Among these semiconductors, silicon has attracted great interest due to silicon integrated photonic devices including sub-wavelength interconnects, modulators, and emission sources[4,9]. Proposed absorber is based on silicon and it extends silicon photonics to the mid-infrared wavelengths for optoelectronic systems Such an absorber paves the way to the realization of all-silicon based sensors, imagers and spectroscopy applications, and provides chip-scale integration compatible with CMOS technology
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