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 surveillanceofconcealed 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]
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| Name | Chemical formula | Groups | Band gap (300 K) |
|---|---|---|---|
| Mercury cadmium telluride | Hg1−xCdxTe | II-VI | 0 to 1.5 eV |
| Mercury zinc telluride | Hg1−xZnxTe | II-VI | 0.15 to 2.25 eV |
| Lead selenide | PbSe | IV-VI | 0.27 eV |
| Lead(II) sulfide | PbS | IV-VI | 0.37 eV |
| Lead telluride | PbTe | IV-VI | 0.32 eV |
| Indium arsenide | InAs | III-V | 0.354 eV |
| Indium antimonide | InSb | III-V | 0.17 eV |
| Gallium antimonide | GaSb | III-V | 0.67 eV |
| Cadmium arsenide | Cd3As2 | II-V | 0.5 to 0.6 eV |
| Bismuth telluride | Bi2Te3 | 0.21 eV | |
| Tin telluride | SnTe | IV-VI | 0.18 eV |
| Tin selenide | SnSe | IV-VI | 0.9 eV |
| Silver(I) selenide | Ag2Se | 0.07 eV | |
| Magnesium silicide | Mg2Si | II-IV | 0.79 eV[26] |
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