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 -degrees polished edge detector, the integrated quantum efficiency for crossed grating detectors of mesa size as small as 45 mum is about fo ur times larger with a waveguide included, and two times larger withou t a waveguide. Furthermore, the importance of a high conductivity grat ing metal, the use of crossed gratings instead of lamellar gratings, a s well as of a dielectric reflector is demonstrated. To show the super ior coupling efficiency, the detectivity is measured for a detector wi th a crossed grating and a waveguide, and of mesa size 500 mum, result ing in D = 1.4 x 10(11) cm Hz1/2 W-1 at 77 K operating temperature wi th the detector shielded from background radiation.