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Narrow-gap semiconductor
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<p>Narrow-gap semiconductors are <a href="/facts/Semiconducting/zFf3mGTE">semiconducting</a> materials with a magnitude of bandgap that is smaller than 0.7 eV, which corresponds to an infrared absorption cut-off <a href="/facts/Wavelength/kcJU0ymz">wavelength</a> over 2.5 micron. A more extended definition includes all semiconductors with bandgaps smaller than <a href="/facts/Silicon/cgWx0hdr">silicon</a> (1.1 eV). Modern <a href="/facts/Terahertz_radiation/729QecPK">terahertz</a>, <a href="/facts/Infrared/44XdJNcc">infrared</a>, and <a href="/facts/Thermography/DWxF0CsD">thermographic</a> technologies are all based on this class of semiconductors. </p><p>Narrow-gap materials made it possible to realize satellite <a href="/facts/Remote_sensing/pj2crmGs">remote sensing</a>, <a href="/facts/Photonic_integrated_circuit/C7skzpMo">photonic integrated circuits</a> for <a href="/facts/Telecommunications/vxoj1cxR">telecommunications</a>, and unmanned vehicle <a href="/facts/Li-Fi/yopv7qBA">Li-Fi</a> systems, in the regime of <a href="/facts/Infrared_detector/pK7SfsEv">Infrared detector</a> and <a href="/facts/Thermography/DWxF0CsD">thermography</a>. They are also the materials basis for terahertz technology, including <a href="/facts/Airport_security/drWkCyBv">security</a> <a href="/facts/Surveillance/hJhvWdSJ">surveillance</a> of <a href="/facts/Concealment_device/gEplrHFW">concealed</a> <a href="/facts/Weapon/fV9QfoBh">weapon</a> uncovering, safe medical and industrial imaging with <a href="/facts/Terahertz_tomography/M2d1UxKy">terahertz tomography</a>, as well as dielectric <a href="/facts/Wakefield_accelerator/8AWHASED">wakefield accelerators</a>. Besides, <a href="/facts/Thermophotovoltaics/kVRzI39d">thermophotovoltaics</a> embedded with narrow-gap semiconductors can potentially use the traditionally wasted portion of <a href="/facts/Solar_energy/YBSajyN4">solar energy</a> that takes up ~49% of the sun light spectrum. Spacecraft, deep ocean instruments, and vacuum physics setups use narrow-gap semiconductors to achieve <a href="/facts/Cryocooler/7cs7ygf2">cryogenic cooling</a>. </p>