Browsing by Subject "Nanophotonics and plasmonics"

Now showing 1 - 3 of 3

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All-silicon ultra-broadband infrared light absorbers
(Nature Publishing Group, 2016) Gorgulu, K.; Gok, A.; Yilmaz, M.; Topalli, K.; Blylkll, N.; Okyay, Ali Kemal
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.
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Disordered nanohole patterns in metal-insulator multilayer for ultra-broadband light absorption: atomic layer deposition for lithography free highly repeatable large scale multilayer growth
(Nature Publishing Group, 2017) Ghobadi, A.; Hajian, H.; Dereshgi, S. A.; Bozok, B.; Butun, B.; Özbay, Ekmel
In this paper, we demonstrate a facile, lithography free, and large scale compatible fabrication route to synthesize an ultra-broadband wide angle perfect absorber based on metal-insulator-metal-insulator (MIMI) stack design. We first conduct a simulation and theoretical modeling approach to study the impact of different geometries in overall stack absorption. Then, a Pt-Al2O3 multilayer is fabricated using a single atomic layer deposition (ALD) step that offers high repeatability and simplicity in the fabrication step. In the best case, we get an absorption bandwidth (BW) of 600 nm covering a range of 400 nm-1000 nm. A substantial improvement in the absorption BW is attained by incorporating a plasmonic design into the middle Pt layer. Our characterization results demonstrate that the best configuration can have absorption over 0.9 covering a wavelength span of 400 nm-1490 nm with a BW that is 1.8 times broader compared to that of planar design. On the other side, the proposed structure retains its absorption high at angles as wide as 70°. The results presented here can serve as a beacon for future performance enhanced multilayer designs where a simple fabrication step can boost the overall device response without changing its overall thickness and fabrication simplicity. © 2017 The Author(s).
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Lithography-free planar band-pass reflective color filter using a series connection of cavities
(Nature Publishing Group, 2019-01) Ghobadi, Amir; Hajian, Hodjat; Soydan, Mahmut Can; Bütün, Bayram; Özbay, Ekmel
In this article, a lithography-free multilayer based color flter is realized using a proper series connection of two cavities that shows relatively high efciency, high color purity, and a wide view angle. The proposed structure is a metal-insulator-metal-insulator-semiconductor (MIMIS) design. To optimize the device performance, at the frst step, transfer matrix method (TMM) modeling is utilized to fnd the right choices of materials for each layer. Simulations are carried out later on to optimize the geometries of the layers to obtain our desired colors. Finally, the optimized devices are fabricated and experimentally characterized to evaluate our modelling fndings. The characterization results of the fabricated samples prove the successful formation of efcient and wide view angle color flters. Unlike previously reported FP based designs that act as a band-stop flter in refection mode (absorbing a narrow frequency range and refecting the rest of the spectrum), this design generates a specifc color by refecting a narrow spectral range and absorbing the rest of the spectrum. The fndings of this work can be extended to other multilayer structures where an efcient connection of cavities in a tandem scheme can propose functionalities that cannot be realized with conventional FP resonators.