Small pitch resonator-QWIP detectors and arrays

Small pixel, high density arrays have many advantages in terms of SWaP-C and detection range. However, it is a challenge for quantum well infrared photodetectors to make into small pixels. The typical grating on the detector needs a large area to be effective. Recently, we introduced the resonator-QWIP for light coupling. This structure utilizes the active absorption volume as a resonator to trap the incident light until it is absorbed. To determine the size limit of this approach, we optimized the detector at different pixel pitches p (= 30, 12, 6, 3 and 2 microns) using 3-dimensional electromagnetic modeling. We found that their quantum efficiency can be kept relatively constant, and an especially large QE of ~80% appears at p = 3 microns at the wavelength of 9.0 microns for an absorption coefficient of 0.2/micron, indicating a great potential for pixel miniaturization. We conducted experiments on test detectors with p = 30, 12 and 6 microns. The set of wafers have two different active layer thicknesses and three different doping densities to create different detector characteristics. The experimental result is in good agreement with the prediction. We are producing 12-μm and 6-μm pitch detector arrays to confirm these test results. The FPAs will have peak wavelengths at either 8.0 or 9.8 microns, all hybridized to 1280x1024, 12-μm pitch ROICs.