Integration of bandpass guided-mode resonance filters with mid-wavelength infrared photodetectors

Guided-mode resonances have been exploited to filter the normal-incidence transmission of mid-infrared wavelengths through a photonic crystal slab. A two-dimensionally periodic structure has been integrated with a quantum dot infrared photodetector to narrow its mid-wavelength infrared photoresponse spectrum. Finite-difference time-domain simulations were employed to extract the filter transmittance, which is dominated by a peak near 6 m. The simulated resonance is linearly tunable with the air-hole radius but it is insensitive to small changes in the incidence angle. To realize this filter, a patterned Ge slab was fabricated on a CaF₂ cladding layer, on the InGaAs/GaAs photodetector. Filters fabricated on a plain GaAs substrate were also characterized by Fourier-transform infrared spectroscopy. This transmittance was consistent with the corresponding simulation, however the resonance peak was degraded in comparison to the filtered photodetector and its associated simulations.