Highly-doped silicon based photonic devices for mid-infrared light absorption

Abstract

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: