Narrow-gap semiconductors are semiconducting materials with a band gap that is comparatively small compared to that of silicon, i.e. smaller than 1.11 eV at room temperature. They are used as infrared detectors or thermoelectrics.
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Dornhaus, R., Nimtz, G., Schlicht, B. (1983). Narrow-Gap Semiconductors. Springer Tracts in Modern Physics 98, ISBN (print) ISBN (online)
Nimtz, G. (1980), Recombination in Narrow-Gap Semiconductors, Physics Reports, 63, 265-300