Cadmium zinc telluride
Encyclopedia
Cadmium zinc telluride, or CZT, is a compound of cadmium
, zinc
and tellurium or, more strictly speaking, an alloy of cadmium telluride
and zinc telluride
. A direct bandgap semiconductor
, it is used in a variety of applications, including radiation
detectors, photorefractive gratings, electro-optic modulator
s, solar cell
s, and terahertz generation and detection. The band gap varies from approximately 1.4 to 2.2 eV, depending on composition.
Radiation detectors using CZT can operate in direct-conversion (or photoconductive) mode at room temperature, unlike some other materials (particularly germanium
) which require liquid nitrogen
cooling. Their relative advantages include high sensitivity for x-rays and gamma-rays, due to the high atomic numbers of Cd and Te, and better energy resolution than scintillator detectors
. CZT can be formed into different shapes for different radiation-detecting applications, and a variety of electrode geometries, such as coplanar grids, have been developed to provide unipolar (electron-only) operation, thereby improving energy resolution.
The material has a high electro-optic coefficient
and transparency in the mid-infrared region, making it a good modulator material for infrared laser
s. The same properties make it useful for detection of terahertz waves.
An additional use is as a substrate material for the epitaxial
growth of mercury cadmium telluride (HgCdTe), an infrared detector
material. Cd0.96Zn0.04Te is almost perfectly lattice matched to LWIR HgCdTe (80% Hg, 20% Cd). However, it is difficult to grow large crystals of fixed composition.
Cadmium Zinc Telluride as a compound was found to be non-toxic at 5g/1kg in an "Acute Oral Limit Toxicity Study" conducted by Toxikon
Cadmium
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...
, zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
and tellurium or, more strictly speaking, an alloy of cadmium telluride
Cadmium telluride
Cadmium telluride is a crystalline compound formed from cadmium and tellurium. It is used as an infrared optical window and a solar cell material. It is usually sandwiched with cadmium sulfide to form a p-n junction photovoltaic solar cell...
and zinc telluride
Zinc telluride
Zinc telluride is a binary chemical compound with the formula ZnTe. This solid is a semiconductor material with band gap of 2.23–2.25 eV. It is usually a P-type semiconductor. Its crystal structure is cubic, like that for sphalerite and diamond....
. A direct bandgap semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
, it is used in a variety of applications, including radiation
Radiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
detectors, photorefractive gratings, electro-optic modulator
Electro-optic modulator
Electro-optic modulator is an optical device in which a signal-controlled element displaying electro-optic effect is used to modulate a beam of light. The modulation may be imposed on the phase, frequency, amplitude, or polarization of the modulated beam...
s, solar cell
Solar cell
A solar cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect....
s, and terahertz generation and detection. The band gap varies from approximately 1.4 to 2.2 eV, depending on composition.
Radiation detectors using CZT can operate in direct-conversion (or photoconductive) mode at room temperature, unlike some other materials (particularly germanium
Germanium
Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....
) which require liquid nitrogen
Liquid nitrogen
Liquid nitrogen is nitrogen in a liquid state at a very low temperature. It is produced industrially by fractional distillation of liquid air. Liquid nitrogen is a colourless clear liquid with density of 0.807 g/mL at its boiling point and a dielectric constant of 1.4...
cooling. Their relative advantages include high sensitivity for x-rays and gamma-rays, due to the high atomic numbers of Cd and Te, and better energy resolution than scintillator detectors
Scintillator
A scintillator is a special material, which exhibits scintillation—the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e., reemit the absorbed energy in the form of light...
. CZT can be formed into different shapes for different radiation-detecting applications, and a variety of electrode geometries, such as coplanar grids, have been developed to provide unipolar (electron-only) operation, thereby improving energy resolution.
The material has a high electro-optic coefficient
Electro-optic effect
An electro-optic effect is a change in the optical properties of a material in response to an electric field that varies slowly compared with the frequency of light...
and transparency in the mid-infrared region, making it a good modulator material for infrared laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
s. The same properties make it useful for detection of terahertz waves.
An additional use is as a substrate material for the epitaxial
Epitaxy
Epitaxy refers to the deposition of a crystalline overlayer on a crystalline substrate, where the overlayer is in registry with the substrate. In other words, there must be one or more preferred orientations of the overlayer with respect to the substrate for this to be termed epitaxial growth. The...
growth of mercury cadmium telluride (HgCdTe), an infrared detector
Infrared detector
An infrared detector is a photodetector that reacts to infrared radiation. The two main types of detectors are thermal and photonic.The thermal effects of the incident IR radiation can be followed through many temperature dependent phenomena....
material. Cd0.96Zn0.04Te is almost perfectly lattice matched to LWIR HgCdTe (80% Hg, 20% Cd). However, it is difficult to grow large crystals of fixed composition.
Cadmium Zinc Telluride as a compound was found to be non-toxic at 5g/1kg in an "Acute Oral Limit Toxicity Study" conducted by Toxikon