Indium antimonide is a narrow-gap semiconductor made of indium and antimony, with chemical formula . Its small band gap permits absorption of comparatively low-energy infrared photons, making it useful in infrared detection.
For an ideal interband threshold, must reach the gap; actual detector response also depends on optical coupling, carrier collection and temperature. Thermal excitation across a small band gap can supply unwanted carriers, so an operating detector's dark current is an essential measurement alongside quantum efficiency. [ref]
https://www.ioffe.ru/SVA/NSM/Semicond/InSb/. Ioffe Institute semiconductor archive, InSb: band structure and physical-property data
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