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). Modern terahertz, infrared, and thermographic technologies are all based on this class of semiconductors.
Narrow-gap materials made it possible to realize satellite remote sensing,Lovett, D. R. Semimetals and narrow-bandgap semiconductors; Pion Limited: London, 1977; Chapter 7. photonic integrated circuits for telecommunications, and unmanned vehicle Li-Fi systems, in the regime of Infrared detector and thermography. They are also the materials basis for terahertz technology, including security surveillance of concealed weapon uncovering,"Space in Images – 2002–06 – Meeting the team".Winner of the 2003/04 Research Councils' Business Plan Competition – 24 February 2004. epsrc.ac.uk. 27 February 2004 safe medical and industrial imaging with terahertz tomography, as well as dielectric wakefield accelerators. 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. Spacecraft, deep ocean instruments, and vacuum physics setups use narrow-gap semiconductors to achieve cryogenic cooling.
List of narrow-gap semiconductors
{| class="wikitable" |- !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 |- | Tellurium | Te | VI | ~0.3 eV |- | Lead telluride | PbTe | IV-VI | 0.32 eV |- | Magnetite | Fe3O4 | Transition Metal-VI | 0.14 eV |- | Indium arsenide | InAs | III-V | 0.354 eV |- | Alpha Tin | Sn | IV | 0.08-0.1 eV |- | Indium antimonide | InSb | III-V | 0.17 eV |- |Gallium antimonide | GaSb | III-V | 0.67 eV - 0.79 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
See also List of semiconductor materials Wide-bandgap semiconductor
References
Further reading Dornhaus, R., Nimtz, G., Schlicht, B. (1983). Narrow-Gap Semiconductors. Springer Tracts in Modern Physics 98, (print) (online)