Fano Resonance Enhanced Infrared Absorption for Infrared Photodetectors

We report spectrally selective IR absorption enhancement in the defect-free photonic crystal cavities, via Fano resonances. For a symmetric slab structure (air-slab-air membrane) with an absorptive layer in the center of the slab, enhanced absorption can be observed with enhancement factor ~180 for certain range of r/a values at wavelength of 4 μm. Similar results can also be achieved in an asymmetric slab structure (air-slab-semiconductor substrate), where higher index substrate is feasible for the proposed IR detectors, with optimized design. This important feature ensures flexible design for infrared photodetectors incorporating photonic crystal cavities. Detailed simulations were carried out to understand the design trade-offs on the key parameters, such as the substrate index, the absorption layer thickness, and the air hole radius.