Efficiency of grating coupled AlGaAs/GaAs quantum well infrared detectors

The efficiency of grating coupling of radiation into the quantum well infrared detector is studied experimentally, with special emphasis on the influence of detector mesa size. It is found that compared to a 45° polished edge detector, the integrated quantum efficiency for crossed grating detectors of mesa size as small as 45 μm is about four times larger with a waveguide included, and two times larger without a waveguide. Furthermore, the importance of a high conductivity grating metal, the use of crossed gratings instead of lamellar gratings, as well as of a dielectric reflector is demonstrated. To show the superior coupling efficiency, the detectivity is measured for a detector with a crossed grating and a waveguide, and of mesa size 500 μm, resulting in D*=1.4×1011 cm Hz1/2 W−1 at 77 K operating temperature with the detector shielded from background radiation.