Charge Transfer Devices for Infrared Imaging

Abstract

A wide variety of infrared photodetectors has been developed for use in thermal imaging systems operating in either the 3–5 μm or 8–12 μm atmospheric windows. The detectors of most interest include photovoltaic InSb, photoconductive Hg _x Cd_{1 − x} Te, photovoltaic Pb _x Sn_{1 − x} Te and various extrinsic photoconductors fabricated by incorporating deep dopants into Ge and Si. Quantum efficiencies for the intrinsic photodetectors are typically above 50%. With sufficient cooling and terrestrial backgrounds, most of these detectors combined with low noise preamplifiers can provide background limited performance (BLIP) for the signal frequencies of interest to thermal imaging systems which use a linear array of detectors in a parallel scan mode (see Fig. 6.1a). Some of them (notably photoconductive Hg_{1 − x} Cd _x Te) are also suitable for 8–12 μm serial scan systems which use time delay and integration (TDI) (see Fig. 6.1b).