Raytheon Vision Systems (RVS, Goleta, CA) in collaboration with HRL Laboratories (Malibu, CA) is contributing to the maturation and manufacturing readiness of third-generation, dual-color, HgCdTe infrared staring focal plane arrays (FPAs). This paper will highlight data from the routine growth and fabrication of 256 ϫ 256 30-µm unit-cell staring FPAs that provide dual-color detection in the mid-wavelength infrared (MWIR) and long wavelength infrared (LWIR) spectral regions. The FPAs configured for MWIR/MWIR, MWIR/LWIR, and LWIR/LWIR detection are used for target identification, signature recognition, and clutter rejection in a wide variety of space and ground-based applications. Optimized triple-layer heterojunction (TLHJ) device designs and molecular beam epitaxy (MBE) growth using in-situ controls has contributed to individual bands in all dual-color FPA configurations exhibiting high operability (>99%) and both performance and FPA functionality comparable to state-of-the-art, single-color technology. The measured spectral cross talk from out-of-band radiation for either band is also typically less than 10%. An FPA architecture based on a single-mesa, single-indium bump, and sequential-mode operation leverages current single-color processes in production while also providing compatibility with existing second-generation technologies.

Raytheon Vision Systems (RVS) is developing two-color, large-format infrared FPAs to support the US Army's Third Generation FLIR systems**. RVS has produced 640 x 480 two-color FPAs with a 20 µm pixel pitch. Work is also underway to demonstrate a 1280 x 720 two-color FPA in 2005. The FPA architecture has been designed to achieve nearly simultaneous temporal detection of the spectral bands while being producible for pixel dimensions as small as 20 microns. Raytheon's approach employs a readout integrated circuit (ROIC) with Time Division Multiplexed Integration (TDMI). This ROIC is coupled to bias-selectable two-color detector array with a single contact per pixel. The twocolor detector arrays are fabricated from MBE-grown HgCdTe triple layer heterojunction (TLHJ) wafers. The single indium bump design is producible for 20 µm unit cells and exploits mature fabrication processes that are in production at RVS for Second Generation FPAs. This combination allows for the high temporal and spatial color registration while providing a low-cost, highly producible and robust manufacturing process.High-quality MWIR/LWIR (M/L) 640 x 480 TDMI FPAs with have been produced and imaged from multiple fabrication lots. These FPAs have LWIR cutoffs ranging to 11 µm at 78K. These 20 µm pixel FPAs have demonstrated excellent sensitivity and pixel operabilities exceeding 99%. NETDs less than 25 mK at f/5 have been demonstrated for both bands operating simultaneously.

For small pixel, infrared (IR) focal plane arrays (FPAs), Raytheon Vision Systems' architecture for integrated, dual-band detectors uses the sequential mode of the n-p ϩ -n configuration. There is a single indium bump per pixel, leaving the p ϩ layer floating, and the operating polarity of the bias selects the spectral sensitivity by reverse-biasing the active p-n junction. Photogenerated minority carriers in the absorber layer of the forward-biased inactive photodiode are lost through recombination. This paper is the first report of a new optical crosstalk mechanism that occurs in sequential-mode, dual-band detectors. In the long-wavelength mode under out-of-band, short-wavelength illumination, radiative recombination yields emission near the bandgap energy of the shortwavelength absorber layer, resulting in a spurious short-wavelength response that appears as spectral crosstalk. We present experimental and device modeling results on the spectral crosstalk in molecular-beam-epitaxy-grown HgCdTe arrays with the cutoff wavelength of both bands in the 4-5-µm range.

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