Indium antimonide

Indium antimonide is a narrow gap semiconductor material from the III-V group used in infrared detectors, including thermal imaging cameras, FLIR systems, infrared homing missile guidance systems, and in infrared astronomy. The indium antimonide detectors are sensitive between 1-5 µm wavelengths. Indium antimonide was a very common detector in the old, single-detector mechanically scanned thermal imaging systems. Another application is as terahertz radiation source as it is a strong Photo-dember emitter.

Indium antimonide is a crystalline compound made from the elements indium and antimony. It has the appearance of dark grey silvery metal pieces or powder with vitreous lustre. When subjected to temperatures over 500 °C, it melts and decomposes, liberating antimony and antimony oxide vapors.

Indium antimonide photodiode detectors are photovoltaic, generating electric current when subjected to infrared radiation. InSb has high quantum efficiency (80-90%). Its drawback is a high instability over time; the detector characteristics tend to drift over time, and between cooldowns, requiring periodic recalibrations, increasing the complexity of the imaging system. Due to their instability, InSb detectors are rarely used in metrology applications. This added complexity is worthwhile where extreme sensitivity is required, e.g. in long-range military thermal imaging systems. InSb detectors also require cooling, as they have to operate at cryogenic temperatures (typically 80 K). However, large arrays (up to 1024x1024 pixels) are available. HgCdTe and PtSi are materials with similar use.

A layer of indium antimonide sandwiched between layers of aluminium indium antimonide can act as a quantum well. This approach is studied in order to construct very fast transistors. Bipolar transistors operating at frequencies up to 85 GHz were constructed from indium antimonide in the late 1990s. Field effect transistors operating at over 200 GHz have been reported more recently (Intel/QinetiQ). Some models suggest terahertz frequencies are achievable with this material. Indium antimonide semiconductors are also capable of operating with voltages under 0.5 V, reducing their power requirements. 

History
InSb crystals have been grown by slow cooling from liquid melt at least since 1954.

Physics
It is a narrow gap semiconductor with an energy band gap equal to 0.17 eV at 300 K and 0.23 eV at 80 K. The crystal structure is zincblende with a 0.648 nm lattice constant.

The undoped semiconductor possesses the largest ambient temperature electron mobility (7.8 m2V-1s-1), electron velocity, and ballistic length (up to 0.7 μm at 300 K) of any known semiconductor except possibly for carbon nanotubes.

Alloys which have been studied include AlInSb, InGaSb, and InAsSb.

Growth Methods
InSb can be grown by solidifying a melt from the liquid state, or epitaxially by liquid phase epitaxy, hot wall epitaxy or molecular beam epitaxy. It can also be grown from organometallic compounds by MOVPE.

Device Applications

 * thermal imager detectors using photodiodes or photoelectromagnetic detectors
 * magnetic sensors using magnetoresistance or the Hall effect
 * fast transistors