QWIP FPAs for high-performance thermal imaging

System properties of focal plane array (FPA) cameras based on GaAs/AlGaAs quantum well infrared photodetectors (QWIPs) operating in the long-wavelength infrared are analyzed. Due to the limited charge storage capacity of available readout circuits, a small photoconductive gain improves the noise-equivalent temperature difference (NE Delta T) of the sensor. We have demonstrated several camera systems based on conventional photoconductive QWIPs with NE Delta T < 10 mK and NE Delta T < 20 mK for FPAs with 256 x 256 and 640 x 512 pixels, respectively. A small photoconductive gain is obtained by operating the QWIP at very small electric fields ( < 3 kV/cm). Finally, we discuss the possibility of reducing the NE Delta T even further by using QWIP structures in which the photoexcited carrier mean free path is controlled by the incorporation of additional epitaxial layers. We thus obtain a high detectivity at very small signal and noise currents, which is useful in particular for large arrays with reduced pixel sizes. In addition, these detectors are shot-noise limited since the recombination noise is suppressed. The performance of FPA sensors based on these detectors will be addressed. (C) 2000 Elsevier Science B.V. All rights resented.