Values of the aspect ratio for trenches etched into HgCdTe by an electron cyclotron resonance (ECR) plasma containing hydrogen and argon are limited by the phenomenon of etch lag. Modeling this plasma as an ion assisted, reactiveetching process leads to a set of conditions that greatly reduces etch lag. Use of these new process conditions produces trenches with aspect ratios greater than 3, widths less than 3 m, and depths in excess of 15 m.

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High-performance 20-mm unit-cell two-color detectors using an n-p 1 -n HgCdTe triple-layer heterojunction (TLHJ) device architecture grown by molecular beam epitaxy (MBE) on (211)-oriented CdZnTe substrates with midwavelength (MW) infrared and long wavelength (LW) infrared spectral bands have been demonstrated. Detectors with nominal MW and LW cut-off wavelengths of 5.5 mm and 10.5 mm, respectively, exhibit 78 K LW performance with .70 % quantum efficiency, reverse bias dark currents below 300 pA, and RA products (zero field of view, 150-mV bias) in excess of 1 3 10 3 Vcm 2 . Temperaturedependent current-voltage (I-V) detector measurements show diffusion-limited LW dark current performance extending to temperatures below 70 K with good operating bias stability (150 mV 6 50 mV). These results reflect the successful implementation of MBE-grown TLHJ detector designs and the introduction of advanced photolithography techniques with inductively coupled plasma (ICP) etching to achieve high aspect ratio mesa delineation of individual detector elements with benefits to detector performance. These detector improvements complement the development of high operability large format 640 3 480 and 1280 3 720 two-color HgCdTe infrared focal plane arrays (FPAs) to support third generation forward looking infrared (FLIR) systems.

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HgCdTe offers significant advantages over other similar semiconductors, which has made it the most widely utilized variable-gap material in infrared (IR) focal plane array (FPA) technology. HgCdTe hybrid FPAs consisting of two-dimensional detector arrays that are hybridized to Si readout circuits (ROIC) are the dominant technology for second-generation infrared systems. However, one of the main limitations of the HgCdTe materials system has been the size of lattice-matched bulk CdZnTe substrates, used for epitaxially grown HgCdTe, which have been limited to 30 cm 2 in production. This size limitation does not adequately support the increasing demand for larger FPA formats which now require sizes up to 2048 3 2048, and only a single die can be printed per wafer. Heteroepitaxial Si-based substrates offer a cost-effective technology that can be scaled to large wafer sizes and further offer a thermalexpansion-matched hybrid structure that is suitable for large format FPAs. This paper presents data on molecular-beam epitaxy (MBE)-grown HgCdTe/Si wafers with much improved materials characteristics than previously reported. We will present data on 4-and 6-in diameter HgCdTe both with extremely uniform composition and extremely low defects. Large-diameter HgCdTe/Si with nearly perfect compositional uniformity and ultra low defect density is essential for meeting the demanding specifications of large format FPAs.