GRATING-COUPLED MULTICOLOR QUANTUM-WELL INFRARED PHOTODETECTORS

Gratings of different period spacings are fabricated on quantum well i nfrared photodetectors having two-stack multiple quantum wells (MQW) t o determine the grating coupling efficiency in multicolor detection. T he peak wavelength of each MQW is 4.8 and 9.4 mu m, respectively, cove ring the two atmospheric windows. 2D gratings of box-shaped cavities w ith grating period either in 3 or 4.6 mu m spacing are used to coupled normal incident light into the detector. Comparing detectors with and without gratings at either normal or 45 degrees facet incidence, the detectors with an optimized grating show efficient light coupling for both wavelengths due to the fact that the longer wavelength in the pre sent case is an integral multiple of the shorter wavelength. The optim ized long wavelength grating couples the shorter wavelength through ad ditional higher orders of diffraction. (C) 1995 American Institute of Physics.