Absorption enhancement in all-semiconductor plasmonic cavity integrated THz quantum well infrared photodetectors.

The light coupling properties of all-semiconductor plasmonic cavity integrated THz quantum well infrared photodetectors were studied for absorption enhancement of the quantum wells. The all-semiconductor plasmonic cavity is constructed by heavily doped GaAs with a plasmonic behavior in the THz regime. The plasmonic behavior of GaAs was thoroughly studied by taking into account the carrier density dependent effective mass of electrons. An optimal doping level for GaAs to be the most metallic is selected since the plasma frequency of the doped GaAs varies nonmonotonically with the carrier density. By tuning the absorption competition between the quantum wells and the doped GaAs meanwhile keeping the system at a critical coupling status, the absorptance of the quantum wells is prominently enhanced by 13.2 times compared to that in a standard device. The all-semiconductor plasmonic cavity integrated quantum well photodetectors can be polarization sensitive (polarization extinction ratio > 900) when the plasmonic cavity is shaped into an anisotropic form. The good tolerance of the incident angle is favored for wide-field infrared detection. The GaAs plasmonic cavities are demonstrated to be effective when integrated at a pixel level, indicating a good compatibility with focal plane arrays.