Plasmonic-coupled quantum dot photodetectors for mid-infrared photonics.

A plasmonic-coupled, InAs-based quantum dot photodetector fabricated for mid-wave infrared photonics is reported. The detector is designed to provide a broadband absorption [full width at half maximum (FWHM) ≳ 2 µm] peaked at ∼5.5 µm, corresponding to transitions from the ground state of the quantum dot to the quasi-continuum resonance state above the quantum well. From the coupling of this transition to the surface plasma wave (SPW) excited by an Au film atop the detector, fabricated with a 1.5 µm-period, 2-dimensional array of square holes, a narrowband SPW enhancement peaked at 4.8 µm with an FWHM less than 0.5 µm is achieved. At ∼90 K, a peak responsivity enhanced ∼5× by the plasmonic coupling is observed. Simulation reveals that this enhancement corresponds to collecting ∼6% of the incident light; ∼40% of the total absorption by the SPW excitation at the peak wavelength.