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 (NEΔT) of the sensor. We have demonstrated several camera systems based on conventional photoconductive QWIPs with View the MathML source and View the MathML source for FPAs with 256×256 and 640×512 pixels, respectively. A small photoconductive gain is obtained by operating the QWIP at very small electric fields (View the MathML source). Finally, we discuss the possibility of reducing the NEΔT 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.