Browsing by Subject "Refractive index sensing"

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Open Access
High-conductivity silicon based spectrally selective plasmonic surfaces for sensing in the infrared region
(Institute of Physics Publishing, 2017) Gorgulu, K.; Gok, A.; Yilmaz, M.; Topalli K.; Okyay, Ali Kemal
Plasmonic perfect absorbers have found a wide range of applications in imaging, sensing, and light harvesting and emitting devices. Traditionally, metals are used to implement plasmonic structures. For sensing applications, it is desirable to integrate nanophotonic active surfaces with biasing and amplification circuitry to achieve monolithic low cost solutions. Commonly used plasmonic metals such as Au and Ag are not compatible with standard silicon complementary metal-oxide-semiconductor (CMOS) technology. Here we demonstrate plasmonic perfect absorbers based on high conductivity silicon. Standard optical lithography and reactive ion etching techniques were used for the patterning of the samples. We present computational and experimental results of surface plasmon resonances excited on a silicon surface at normal and oblique incidences. We experimentally demonstrate our absorbers as ultra-low cost, CMOS-compatible and efficient refractive index sensing surfaces. The experimental results reveal that the structure exhibits a sensitivity of around 11 000 nm/RIU and a figure of merit of up to 2.5. We also show that the sensing performance of the structure can be improved by increasing doping density.
Open Access
Highly-doped silicon based photonic devices for mid-infrared light absorption
(2017-07) Görgülü, Kazim
Electromagnetic wave absorbers have the potential to enable important applications in the mid-infrared wavelength range such as thermal imaging and infrared spectroscopy. The choice of absorbing material has signi cant implications for the ultimate utility of any photonic device or structure. So far, traditional metals are employed as common absorbing materials, especially in metamaterial designs. However, many of these metals react with the atmosphere or water, limiting their utility for a wide range of applications. There are many materials, other than conventional metallic components, that exhibit lossy properties and provide advantages in device performance, design exibility, fabrication, integration, and tunability. Here, we investigate highly doped silicon as an e cient absorbing material for the mid-infrared regime. The absorption is achieved by the free carriers in the silicon which can be spectrally tuned by controlling its carrier concentration. Most of the resonant absorbers su er from narrow operating absorption waveband. A common approach is to use multiple resonance centers to increase bandwidth. However, the number of resonators combined within the same unit cell is limited. We propose highly doped silicon based absorbers with a patterned silicon-on-insulator substrate that provide enhanced bandwidth without compromising absorption performance. Broadband absorption is achieved by the combined e ects of bulk absorption, and vibrational and plasmonic absorption resonances. Moreover, we investigate black silicon concept for mid-infrared regime. The structures investigated unveil wideband and e cient absorbers. An analytical description of the wave propagation in black silicon texture is presented, showing agreement with the experiment and the computational analysis. Some other applications, such as selective thermal emitters and detectors, and bio-chemical and refractive index sensors, require narrow absorption bands. Plasmonic absorbers typically have narrow resonance bands and they can be utilized in highly sensitive detection schemes. Traditional metals are common materials for these applications. However, apart from their fabrication challenges, they have extremely large, negative permittivity. This feature of metals signi cantly limits their plasmonic mode con nement in the mid-infrared regime. In this regime, highly doped silicon is a promising plasmonic material for sensing applications owing to its suitable plasma frequency. Here, we demonstrate plasmonic perfect absorbers based on high conductivity silicon and investigate refractive index sensing performance of the absorbers. Keywords: