InSb stands for Indium Antimony (or Antimonide). It is a type of semiconductor. More specifically a type of Microbolometer sensor used in some cooled thermal cameras.
Indium Antimonide is a crystalline semiconductor made of antimony and indium. It belongs to the III-V group and is a narrow gap semiconductor material. Detectors made of indium antimonide are sensitive between a wavelength of 1-5 µm [MWIR].
InSb sensors must be cryogenically cooled and have much lower temperature requirements than MCT or Infiniti's line of X-HOT sensors.
Unlike Microbolometer Type detectors that are Photoresistant. InSb detectors are Photovoltaic. Which means that they generate a small voltage when they are hit with radiation energy, rather than generate a resistance like a microbolometer does.
Undoped InSb possesses the largest ambient-temperature electron mobility (78000 cm2/V⋅s), electron drift velocity, and ballistic length (up to 0.7 μm at 300 K) of any known semiconductor, except for carbon nanotubes.