HgCdTe CCD infrared imager arrays

CCD linear arrays and area arrays are being developed for infrared image detection using HgxCd1-xTe alloy semiconductors operated near 77K temperature. Charge transfer efficiencies (CTE) up to 0.9996 have been achieved on 32-stage p-channel linear shift registers. Area arrays operating in a TDI/MPX mode have displayed CTE values in the 0.995-0.998 range. Most studies have utilized HgCdTe with 4.4-4.7 µm long wavelength cutoff. Dark storage times up to 20 minutes and carrier storage capacities as high as 4.6×10¹¹/cm²have been obtained using HgCdTe with 4.2 µm long wavelength cutoff. Time-delay-and-integrate operation has been demonstrated. Visible light illumination through a transparent electrode decreases flatband voltage, but this effect can be annealed out near 90°C. This multiple flatband voltage phenomenon in unannealed devices can reduce CTE and decrease edge enhancement of electric field in some CCD structures.