InAsSb Hybrid Imager Evaluation

AbstractCurrent research on infrared hybrid focal planes is directed toward devices in whichdetection occurs in a p -n junction formed in an intrinsic narrow energy bandyap semi-conductor, and signal processing is accomplished in a Si CCD multiplexer which is electri-cally interfaced to the detector array. A hybrid array such as this, where the detectorformat is a 32 x 32 matrix, has been fabricated. The active material is backside-illumi -nated InAsSb which has been planar processed and fully passivated. The cutoff wavelengthis 4.0 pm at the operating temperature of 77K. The CCD is four phase with a two levelpolysilicon yate structure. The signal input is via direct injection with an option for dcsuppression. Operation of the focal plane in a staring mode that uses dc suppression isdiscussed. Data derived from the video output is presented; this includes responsivity anddetectivity. Off focal plane non -uniformity compensation is also discussed. Displays ofthermal images utilizing processed data from the hybrid focal plane array will be shown.IntroductionA demand for high performance, high density, nigher operating temperature imaging arrayswhich can be produced in quantity exists. In order to address these needs, a "common"detection technology approach has been adopted; this permits a variety of system require-ments to be satisfied with a maximum of overlap in the technology used. This approach usesa hybrid structure that consists of three components: a photovoltaic detector, which isbackside - illuminated through a transparent substrate; a Si CCD multiplexer, which alsoserves to integrate the signal; and an In interconnect technology, which electrically andphysically joins the detector array to the multiplexer.Changes in detector material and CCD multiplexer input cell allow operation in anyportion of the 3 - 12 pm spectral region for both high and low background. Both epitaxialInAsl_xSbx /GaSb and Hgl_xCdxTe /CdTe are under intensive development for use in this commonapproach; the former for applications in the 3 - 5 um spectral band, the latter for bothmid and far IR spectral bands. Details of current detector performance for these systemshas been given elsewhere (1,2). Photocurrent from the detector is injected into an induceddrain FET (which may be the CCD itself if no "front end" signal processing is desired).The signal may then be processed according to the application, including dc suppression,gain reduction, and ac coupling. This paper reports on the construction and imaging with acommon focal plane array that has InAsSb as the detector material. The focal plane geome-try is a 32 x 32 matrix which is operated in a staring mode.Hybrid ComponentsDetectorsDetectors were fabricated from InAsl_XSbx/ GaSb, grown by liquid phase epitaxy withx = 0.11 (lattice matched system). Fabrication of the detectors is a planar process thatuses Be ion implantation with CVD SiO2 as an insulator (3). The spectral response of thesedetectors is from 1.6 (cut -on of the transparent GaSb substrate) to 3.95 um at 77K, with aquantum efficiency of about 80 percent. At this tpemperature the RoA of at least ninetypecent of the 1024 detectors is in excess of 10