Narrow-gap semiconductors are semiconducting materials with a magnitude of bandgap that is smaller than 0.7 eV, which corresponds to an infrared absorption cut-off wavelength over 2.5 micron.
A more extended definition includes all semiconductors with bandgaps smaller than silicon (1.1 eV).
Narrow-gap materials made it possible to realize satellite remote sensing,[6] photonic integrated circuits for telecommunications,[7][8][9] and unmanned vehicle Li-Fi systems,[10] in the regime of Infrared detector and infrared vision.
[19][20][21] Besides, thermophotovoltaics embedded with narrow-gap semiconductors can potentially use the traditionally wasted portion of solar energy that takes up ~49% of the sun light spectrum.
[22][23] Spacecraft, deep ocean instruments, and vacuum physics setups use narrow-gap semiconductors to achieve cryogenic cooling.