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Information about Cadmium Telluride

Cadmium telluride
Other namesIrtran-6
Identifiers
CAS number1306-25-8
Properties
Molecular formulaCdTe
Molar mass240.01 g/mol
Density5.85 g/cm³
Melting point 1092 °C
Boiling point 1130 °C
Solubility in other solventsinsoluble
Except where noted otherwise, data are given for
materials in their standard state
(at 25 C, 100 kPa)


Cadmium telluride (CdTe) is a crystalline compound formed from cadmium and tellurium with a zinc blende (cubic) crystal structure (space group F43m). In the bulk crystalline form it is a direct bandgap semiconductor. CdTe is also a strong solar cell material. It is usually sandwiched with cadmium sulfide to form a pn junction photovoltaic solar cell.

Applications

CdTe is a useful material for solar cells (photovoltaics). It is cheaper than silicon, especially in thin-film solar cell technology, but not as efficient. CdTe can be alloyed with mercury to make a versatile infrared detector material (HgCdTe). CdTe alloyed with a small amount of zinc makes an excellent solid-state x-ray and gamma ray detector (CdZnTe).

CdTe is used as an infrared optical material for optical windows and lenses but it has small application and is limited by its toxicity such that few optical houses will consider working with it. An early form of CdTe for IR use was marketed under the trademarked name of Irtran-6 but this is obsolete.

CdTe is also applied for electrooptical modulators. It has highest electrooptical coefficient of the linear electrooptic effect among II-VI compound crystals (r41=r52=r63=6.8*10-12 m/V).

Physical properties

Thermal Properties

Electronic properties

  • The direct band gap is 1.56 eV at 300 K.
  • Electron effective mass 0.11 me
  • Hole effective mass 0.4 me

Optical Properties

CdTe is transparent in the infrared, from close to its band gap energy (=795nm) out to wavelengths greater than 20 µm. The refractive index is 2.649 at 10µm.

Chemical properties

CdTe has very low solubility in water. It is etched by many acids including hydrochloric, and hydrobromic acid, forming (toxic) hydrogen telluride gas.

Cadmium telluride is commercially available as a powder, or as crystals. It can be made into nanocrystals.

Toxicity

Cadmium telluride is toxic. It should not be ingested, nor its dust inhaled, and it should not be handled without appropriate gloves. Please refer to materials safety data sheets for details.

The toxicity is not solely due to the cadmium content. One study found that the highly reactive surface of cadmium telluride quantum dots triggers extensive reactive oxygen damage to the cell membrane, mitochondria, and cell nucleus.[1]

The disposal life-cycle and long term safety of cadmium telleride could become an issue in the large scale commercialization of cadmium telluride solar panels. A document hosted by the U.S. National Institutes of Health[2] dated 2003 discloses that:
Brookhaven National Laboratory (BNL) and the U.S. Department of Energy (DOE) are nominating Cadmium Telluride (CdTe) for inclusion in the National Toxicology Program (NTP). This nomination is strongly supported by the National Renewable Energy Laboratory (NREL) and First Solar Inc. The material has the potential for widespread applications in photovoltaic energy generation that will involve extensive human interfaces. Hence, we consider that a definitive toxicological study of the effects of long-term exposure to CdTe is a necessity.

New Theoretical Model

Making use of the authors' experimental results and the evidence available in the literature, Prof. I.M.Dharmadasa and his co-workers at Sheffield Hallam University in the United Kingdom presented an alternative theoretical model to describe the working scientific mechanism of glass/conducting glass/CdS/CdTe/metal solar cell. This model explains the behaviour of this particular solar cell in terms of a combination of a hetero-junction and a large Schottky barrier at the CdTe/metal interface. In the article, their main experimental observations are compared with the traditionally accepted pn junction model. It is shown that the proposed model explains the experimental results more satisfactorily than the widely used pn junction model. The paper describes the guidelines to further increase the performance efficiencies based on the new model.The full article can be found here: [1]

See also

References

1. ^ [2]
2. ^ [3]

External links

CAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. They are also referred to as CAS numbers, CAS RNs or CAS #s.
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A chemical formula is a concise way of expressing information about the atoms that constitute a particular chemical compound. A chemical formula is also a short way of showing how a chemical reaction occurs.
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Cadmium (IPA: /ˈkædmiəm/) is a chemical element in the periodic table that has the symbol Cd and atomic number 48.
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4, 6
(mildly acidic oxide)
Electronegativity 2.1 (scale Pauling)
Ionization energies
(more) 1st: 869.3 kJmol−1
2nd: 1790 kJmol−1
3rd: 2698 kJmol−1
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Molar mass, symbol M,[1] is the mass of one mole of a substance (chemical element or chemical compound).[2] It is a physical property which is characteristic of each pure substance.
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In physics, density is mass m per unit volume V—how heavy something is compared to its size. A small, heavy object, such as a rock or a lump of lead, is denser than a lighter object of the same size or a larger object of the same weight, such as pieces of
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The melting point of a crystalline solid is the temperature range at which it changes state from solid to liquid. Although the phrase would suggest a specific temperature and is commonly and incorrectly used as such in most textbooks and literature, most crystalline compounds
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boiling point of a liquid is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid.[1][2][3][4]
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Solubility is a physical property referring to the ability for a given substance, the solute, to dissolve in a solvent.[1] It is measured in terms of the maximum amount of solute dissolved in a solvent at equilibrium. The resulting solution is called a saturated solution.
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standard state of a material is its state at 1 bar (100 kilopascals exactly). This pressure was changed from 1 atm (101.325 kilopascals) by IUPAC in 1990.[1] The standard state of a material can be defined at any given temperature, most commonly 25 degrees Celsius,
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CRYSTAL is a quantum chemistry ab initio program, designed primarily for calculations on crystals (3 dimensions), slabs (2 dimensions) and polymers (1 dimension) using translational symmetry, but it can be used for single molecules.[1] It is written by V.R. Saunders, R.
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Cadmium (IPA: /ˈkædmiəm/) is a chemical element in the periodic table that has the symbol Cd and atomic number 48.
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4, 6
(mildly acidic oxide)
Electronegativity 2.1 (scale Pauling)
Ionization energies
(more) 1st: 869.3 kJmol−1
2nd: 1790 kJmol−1
3rd: 2698 kJmol−1
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Sphalerite (ZnS) is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron. When iron content is high it is an opaque black variety, marmatite ((Zn,Fe)S).
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The space group of a crystal is a mathematical description of the symmetry inherent in the structure. The word 'group' in the name comes from the mathematical notion of a group, which is used to build the set of space groups.
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radiative recombination, also called spontaneous emission. In indirect bandgap semiconductors such as crystalline silicon, the momentum of the conduction band minimum and valence band maximum are not the same, so a direct transition across the bandgap does not conserve momentum and
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A semiconductor is a solid that has electrical conductivity in between that of a conductor and that of an insulator, and can be controlled over a wide range, either permanently or dynamically.[1] Semiconductors are tremendously important in technology.
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A solar cell or photovoltaic cell is a device that converts light energy into electrical energy. Sometimes the term solar cell is reserved for devices intended specifically to capture energy from sunlight, while the term photovoltaic cell
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Cadmium sulfide is a chemical compound with the formula CdS. It exists in nature as two different minerals, greenockite and hawleyite.

Greenockite forms hexagonal crystals with the wurtzite structure. It has a yellowish colour with specific gravity of 4.
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A p-n junction is formed by combining P-type and N-type semiconductors together in very close contact. The term junction refers to the region where the two types of semiconductor meet.
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Photovoltaics, or PV for short, is a solar power technology that uses solar cells or solar photovoltaic arrays to convert light from the sun directly into electricity.
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Photovoltaics, or PV for short, is a solar power technology that uses solar cells or solar photovoltaic arrays to convert light from the sun directly into electricity.
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Silicon (IPA: /ˈsɪlɪkən/ or /ˈsɪlɪˌkɑn/, Latin: silicium
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A solar cell or photovoltaic cell is a device that converts light energy into electrical energy. Sometimes the term solar cell is reserved for devices intended specifically to capture energy from sunlight, while the term photovoltaic cell
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2, 1
(mildly basic oxide)
Electronegativity 2.00 (scale Pauling)
Ionization energies 1st: 1007.1 kJ/mol
2nd: 1810 kJ/mol
3rd: 3300 kJ/mol
Atomic radius 150 pm
Atomic radius (calc.
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An infrared detector is a photodetector that reacts to infrared (IR) 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.
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Zinc (IPA: /ˈzɪŋk/, from German: Zink) is a chemical element in the periodic table that has the symbol Zn and atomic number 30.
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X-rays (or Röntgen rays) are a form of electromagnetic radiation with a wavelength in the range of 10 to 0.01 nanometers, corresponding to frequencies in the range 30 PHz to 30 EHz. X-rays are primarily used for diagnostic radiography and crystallography.
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Gamma rays or gamma-ray (denoted as γ) are forms of electromagnetic radiation (EMR) or light emissions of a specific frequency produced from sub-atomic particle interaction, such as electron-positron annihilation and
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