Mercury(II) cadmium(II) telluride

HgCdTe or mercury cadmium telluride (also cadmium mercury telluride, MCT, MerCad Telluride, MerCadTel, MerCaT or CMT) is narrow direct bandgap zincblende II-VI ternary alloy of CdTe and HgTe with a tunable bandgap spanning the shortwave infrared to the very long wave infrared regions. The amount of cadmium (Cd) in the alloy (the alloy composition) can be chosen so as to tune the optical absorption of the material to the desired infrared wavelength. CdTe is a semiconductor with a bandgap of approximately 1.5 eV at room temperature. HgTe is a semimetal, hence its bandgap energy is zero. Mixing these two substances allows one to obtain any bandgap between 0 and 1.5 eV.

HgCdTe has a zincblende structure with two interpenetrating face-centered cubic lattices offset by (1/4,1/4,1/4)a_o in the primitive cell. The cations (Cd or Hg) form the yellow sublattice while the Te anions form the grey sublattice per the adjacent diagram.

The electron mobility of HgCdTe with a large Hg content is very high. Among common semiconductors used for infrared detection, only InSb and InAs surpass electron mobility of HgCdTe at room temperature. At 80 K, the electron mobility of Hg_0.8Cd_0.2Te can be several hundred thousand cm²/(V·s). Electrons also have a long ballistic length at this temperature; their mean free path can be several micrometres.

The intrinsic carrier concentration is given by

${\displaystyle n_{i}(t,x)=(5.585-3.82x+(1.753\cdot 10^{-3})t-1.364\cdot 10^{-3}t\cdot x)\cdot 10^{14}\cdot E_{g}(t,x)^{0.75}\cdot T^{1.5}\cdot e^{\frac {-E_{g}(t,x)\cdot q}{2\cdot k\cdot t}}}$

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