Two-Color Random Reflectors for QWIPs

Random reflectors of a proposed type would be fabricated on the back surfaces of quantum-well infrared photodetectors (QWIPs) to increase the coupling efficiency of infrared light into the QWIPs in two wavelength bands. A reflective surface according to this proposal would comprise an array of square cells, each cell divided into a 2-by-2 array of subcells that would lie at various, partly random depths relative to the nominal flat back surface of the QWIP. The subcells at the various depths would be formed by one of several lithographic processes, depending on the specific design. In comparison with the light-scattering efficiency of crossed-diffraction-grating QWIP light couplers that have been reported previously in NASA Tech Briefs, the light-scattering efficiency of the proposed random reflectors would be less dependent on wavelength; this would be an advantage in QWIP applications in which there are requirements for broad-band or multiband response.