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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The erosion rate of resist during electron cyclotron resonance (ECR) plasma etching of II-VI semiconductors is the limiting factor for the selectivity (values range from 5:1 to 10:1). We have measured the erosion rates of AZ 1529, a commercially available diazonaphthoquinone (DNQ) novolak photoresist, under plasma conditions optimized for etching of the underlying semiconductor and have developed an in-situ technique to "harden" the resist by exposing it to an argon-only ECR plasma. A subsequent standard plasma process can then be used to etch the II-VI material, thereby achieving selectivity values greater than 50:1.

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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The use of silicon as an alternative substrate to bulk CdZnTe for epitaxial growth of HgCdTe for infrared detector applications is attractive because of potential cost savings as a result of the large available sizes and the relatively low cost of silicon substrates. However, the potential benefits of silicon as a substrate have been difficult to realize because of the technical challenges of growing low-defect-density HgCdTe on silicon where the lattice mismatch is $19%. This is especially true for long-wavelength infrared (LWIR) HgCdTe detectors where the performance can be limited by the high ($5 · 10 6 cm -2 ) dislocation density typically found in HgCdTe grown on silicon. The current status of LWIR (9 lm to 11 lm at 78 K) HgCdTe on silicon focal-plane arrays (FPAs) is reviewed. Recent progress is covered including improvements in noise equivalent differential temperature (NEDT) and array operability. NEDT of <25 mK and NEDT operability >99% are highlighted for 640 · 480 pixel, 20-lm-pitch FPAs.

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The use of silicon as a substrate alternative to bulk CdZnTe for epitaxial growth of HgCdTe for infrared (IR) detector applications is attractive because of potential cost savings as a result of the large available sizes and the relatively low cost of silicon substrates. However, the potential benefits of silicon as a substrate have been difficult to realize because of the technical challenges of growing low defect density HgCdTe on silicon where the lattice mismatch is ϳ19%. This is especially true for LWIR HgCdTe detectors where the performance can be limited by the high (ϳ5 ϫ 10 6 cm Ϫ2 ) dislocation density typically found in HgCdTe grown on silicon. We have fabricated a series of long wavelength infrared (LWIR) HgCdTe diodes and several LWIR focal plane arrays (FPAs) with HgCdTe grown on silicon substrates using MBE grown CdTe and CdSeTe buffer layers. The detector arrays were fabricated using Rockwell Scientific's planar diode architecture. The diode and FPA and results at 78 K will be discussed in terms of the high dislocation density (ϳ5 ϫ 10 6 cm 2 ) typically measured when HgCdTe is grown on silicon substrates.