Further Developments Regarding Noise-Reducing Slots in QWIPs

A report presents additional information on the devices described in “Noise-Reducing Slots in Quantum-Well Infrared Photodetectors” (NPO-20518), NASA Tech Briefs, Vol. 25, No. 6 (June 2001), page 6a. To recapitulate: it was proposed that incorporation of suitably dimensioned crossed slots into quantum-well infrared photodetectors (QWIPs) equipped with two-dimensional surface grating light couplers would reduce dark currents and increase detectivities. Going slightly beyond that proposal, the report proposes optionally filling the slots with low-index-of-refraction dielectric material. Going beyond the previous discussion, the report notes that finite-difference solution of the Helmholtz equations for electromagnetic coupling into a slotted QWIP leads to the conclusions that (1) the slotted QWIP acts as an array of leaky waveguides or weakly coupled cavity resonators; (2) coupling can be maximized by choosing the width, spacing, and index of refraction of the slots to obtain resonance at the desired wavelength of operation; and (3) the coupling in such a case is stronger and more broad-band, relative to the coupling into a nonslotted surface-grating QWIP.