No 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-lm 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 cutoff 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-antireflection-coated QE in the 8-10 lm 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.

No abstract

The effects of microvoid defects on the performance of mid-wavelength infrared (MWIR) HgCdTe-based diodes were examined. Molecular beam epitaxy (MBE) was utilized to deposit indium-doped, Hg 0.68 Cd 0.32 Te on 2 cm 9 3 cm, (211)B-oriented, bulk Cd 0.96 Zn 0.04 Te substrates. These epilayers generally exhibited state-of-the-art material properties with a notable exception: high and nonuniform microvoid defect densities (mid 10 4 cm À2 to low 10 6 cm À2 ). Diodes were fabricated by ion implantation of arsenic to form planar p-n junctions. Dark current-voltage (I-V) curves were measured and analyzed as a function of operating temperature. There was an inverse correlation between wafer-level microvoid defect density and device operability. On each wafer, devices with the smallest implants exhibited higher operability than devices with larger implants. By removal of pad metal and examination of defects within each implant area, it was found that the presence of one or more microvoids within the junction usually caused tunneling or other high-current mechanisms. Diodes free from microvoids exhibited diffusion-limited behavior down to 150 K, the test set limit.