Mercury cadmium telluride
The amount of cadmium (Cd) in the alloy can be chosen so as to tune the optical absorption of the material to the desired infrared wavelength.
Hg1−xCdxTe has a zincblende structure with two interpenetrating face-centered cubic lattices offset by (1/4,1/4,1/4)ao in the primitive cell.
Among common semiconductors used for infrared detection, only InSb and InAs surpass electron mobility of HgCdTe at room temperature.
The Auger 1 minority carrier lifetime for intrinsic (undoped) HgCdTe is given by[3] where FF is the overlap integral (approximately 0.221).
In particular, the US air force makes extensive use of HgCdTe on all aircraft, and to equip airborne smart bombs.
HgCdTe detector arrays can also be found at most of the worlds major research telescopes including several satellites.
MWIR HgCdTe cameras can be operated at temperatures accessible to thermoelectric coolers with a small performance penalty.
On the other side, HgCdTe enjoys much higher speed of detection (frame rate) and is significantly more sensitive than some of its more economical competitors.
HgCdTe can be used as a heterodyne detector, in which the interference between a local source and returned laser light is detected.
The main competitors of HgCdTe are less sensitive Si-based bolometers (see uncooled infrared camera), InSb and photon-counting superconducting tunnel junction (STJ) arrays.
Quantum well infrared photodetectors (QWIP), manufactured from III–V semiconductor materials such as GaAs and AlGaAs, are another possible alternative, although their theoretical performance limits are inferior to HgCdTe arrays at comparable temperatures and they require the use of complicated reflection/diffraction gratings to overcome certain polarization exclusion effects which impact array responsivity.
In the future, the primary competitor to HgCdTe detectors may emerge in the form of Quantum Dot Infrared Photodetectors (QDIP), based on either a colloidal or type-II superlattice structure.
Initial laboratory work has shown promising results in this regard and QDIPs may be one of the first significant nanotechnology products to emerge.
Such an electron is collected by a suitable external readout integrated circuits (ROIC) and transformed into an electric signal.
It is not lattice-matched to HgCdTe, but is much cheaper, as it can be grown by epitaxy on silicon (Si) or germanium (Ge) substrates.
In recent years, molecular beam epitaxy (MBE) has become widespread because of its ability to stack up layers of different alloy composition.
