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Chapter 7:
Photoelectromagnetic, Magnetoconcentration, and Dember IR Detectors
Aside from photoconductive detectors and photodiodes, three other junctionless devices have been used for uncooled IR photodetectors: photoelectromagnetic (or PEM) detectors, magnetoconcentration detectors, and Dember effect detectors. Certainly they are niche devices, but they are still in production and used with important applications, including very fast uncooled detectors with long-wavelength IR radiation. The devices have been reviewed by Piotrowski and Rogalski. 7.1 PEM Detectors The first experiments on the PEM effect were performed with Cu2O by Kikoin and Noskov in 1934. Nowak's monograph summarizes the results of his investigations on the PEM effect, which have been replicated worldwide during the last 60 years. For a long time, the PEM effect has been used mostly for InSb room temperature detectors in the middle- and far-IR band. However, the uncooled InSb devices with cutoff wavelength at ≈7 μm exhibit no response in the 8–14 μm atmospheric window and relatively modest performance in the 3–5 μm window. Hg1−xCdxTe and closely related Hg1−xZnxTe and Hg1−xMnxTe alloys made it possible to optimize performance of PEM detectors at any specific wavelength. 7.1.1 PEM effect The PEM effect is caused by diffusion of photogenerated carriers due to the photoinduced carrier in-depths concentration gradient and by deflection of electron and hole trajectories in opposite directions by the magnetic field (Fig. 7.1). If the sample ends are open-circuit in the x -direction, a space charge builds up that gives rise to an electric field along the x axis (open-circuit voltage).
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