Abstract
If we can make wavelength-sized detectors, we approach the limit at which smaller detectors have no further advantage for imaging focal plane arrays with practical (f/1-2) optics. Of course, this must be accomplished without compromising performance—a challenge for 5-μm devices for which the perimeter, the currents of which depend on passivation quality, is very large compared with the area of the device. This paper describes the development of small LWIR HgCdTe detectors and compares dark current performance with that of larger basic devices, as described by “Rule 07”, a well-known rule of thumb which gives the HgCdTe dark-current density characteristics of the best reported diodes as a function of device cut-off wavelength and operating temperature. Low cross-talk requires a fully-depleted absorber layer sufficiently thick to provide adequate quantum efficiency (QE). Preliminary results show dark-current densities are more than a factor of ten below the Rule 07 trend line. With these dark-current densities, the measured ∼40% non-anti-reflection-coated QE in the 8–10 μm region is more than adequate to achieve background-limited performance with the margin under tactical backgrounds for the fast (f/1), diffraction-limited optics required for the small pixels.
Highlights
OF THE PROBLEMDr Nibir Dhar of the Defense Advanced Research Projects Agency (DARPA) presented a keynote SPIE paper ‘‘Advanced Imaging Research and Development at DARPA’’1 in which he discussed the Advanced Wide FOV Architecture for Image Reconstruction and Exploitation (AWARE)-Lambda Scale detector program, which is developing high-performance focal plane arrays (FPA) with pixel dimensions approaching the wavelength scale (Nyquist limit)
Some adjustment of wavelength and thickness was made for the later layers (G-H), because it was clear from the first lots that we did not need such a long wavelength to obtain high quantum efficiency in the 8–10 lm spectral region, even with thin layers
We report the first planar 5 lm-pitch detectors made by ion implantation in molecular beam epitaxy-grown HgCdTe heterostructures
Summary
BACKGROUND AND STATEMENT OF THE PROBLEMDr Nibir Dhar of the Defense Advanced Research Projects Agency (DARPA) presented a keynote SPIE paper ‘‘Advanced Imaging Research and Development at DARPA’’1 in which he discussed the Advanced Wide FOV Architecture for Image Reconstruction and Exploitation (AWARE)-Lambda Scale detector program, which is developing high-performance focal plane arrays (FPA) with pixel dimensions approaching the wavelength scale (Nyquist limit). Our preliminary results show that such devices have dark-current densities more than a factor of ten below the Rule 07 trend line,[2,3] because of their low doping and thin layer structure.
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