An all silicon-based metamaterial for mid-IR energy harvesting

Energy conservation techniques have been widely explored in recent years for several applications: IR camouflage, solar absorbers and for IR thermal harvesting as well. While many absorbers have been demonstrated using plasmonic metal nanoparticles, surface texturing and low density broad band absorbers, they still encounter inevitable drawbacks. The state of art absorbers are either suffering instability over time or bulkiness which limit their practical application. Metamaterials have provided a significant improvement overcoming the aforementioned challenges through introducing ultra-broad band absorbers. However, the urge for CMOS compatible sub-wave length absorber that can be integrated for opto/electronic devices is still a major challenge. We demonstrate a mid IR silicon absorber using doped Silicon/Silicon Hyperbolic Metamaterial (HMM) integrated with sub-wave length Si grating. HMMs are characterized by their hyperboloid dispersion momentum space that provides large density of photonic states. By applying sub-wavelength grating on HMM, light from free space can be coupled to high propagation wave vectors of the hyperbolic modes upon breaking the momentum mismatch restriction, leading to noticeable absorption. We are able to show that an all Si based designed HMM is capable to achieve absorption across the mid IR wavelength range reaching absorption (A) of value 0.9.This proposed CMOS compatible Si-based absorber serves as good candidate for IR thermal harvesting application for on chips purposes.