A design of plasmonic coupler, composed of metal hole arrays and germanium spacer layer, integrated with quantum well infrared photodetector structure is presented. Insertion of germanium spacer layer in this hybrid structure enhances absorption and z-component of electric field in the quantum well absorption region under both substrate-side and air-side illumination configurations. By changing thickness of the germanium spacer layer, the plasmonic resonance wavelengths can be adjusted with peak quantum well response. This plasmonic coupler is believed to be promising to improve performance of quantum well infrared photodetectors.

A broadband cavity architecture for ultra-thin type-II superlattice (T2SL) mid-infrared detectors is designed by exploiting coordinated coupling of the surface plasmon polariton mode and cavity mode in an Au-antenna/detector/highly doped semiconductor ground-plane configuration. By optimizing the doping concentration of the doped semiconductor ground-plane and the size of the antenna, the desired extent of coupling between the modes can be achieved, resulting in enhanced absorption over a broad infrared wavelength band. The absorption in the T2SL active layer in the proposed cavity architecture can be enhanced by nearly 10 times compared with that in the reference structure (without ground-plane and antenna). The cavity architecture is also studied by investigating angular and polarization dependence. This cavity architecture offers potential benefits to type-II superlattice detector performance with minimal growth cost.