Narrow-gap semiconductor

Narrow-gap semiconductors are semiconducting materials with a magnitude of bandgap that is smaller than 0.5 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).[1][2] Modern terahertz,[3] infrared,[4] and thermographic[5] technologies are all based on this class of semiconductors.

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.[11][12] They are also the materials basis for terahertz technology, including security surveillance of concealed weapon uncovering,[13][14][15] safe medical and industrial imaging with terahertz tomography,[16][17][18] as well as dielectric wakefield accelerators.[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] Space crafts, deep ocean instruments, and vacuum physics setups use narrow-gap semiconductors to achieve cryogenic cooling.[24][25]