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Zinc selenide (ZnSe), is a light yellow binary solid compound. It is an intrinsic semiconductor with a band gap of about 2.7 eV at 25 °C. It has a standard enthalpy of formation of 177.6 kJ/mol at 25 °C. It adopts a zincblende lattice structure with lattice constant a=566.8 picometers.
ZnSe rarely occurs in nature. It is found in the mineral stilleite named after Hans Stille.
Applications
- ZnSe is used to form II-VI light-emitting diodes and diode lasers. It emits blue light. It is susceptible to n-type doping with, for instance, halogen elements. P-type doping is more difficult, but can be achieved by introducing nitrogen.
- ZnSe doped with chromium (ZnSe:Cr) has been used as an infrared laser gain medium emitting at about 2.5 µm.[1]
- It is used as an infrared optical material with a remarkably wide transmission wavelength range (0.6 µm to 20 µm). The refractive index is about 2.67 at 550 nm (green), and about 2.40 at 10.6 µm (LWIR). ZnSe is produced as microcrystalline sheets by synthesis from H2Se gas and zinc vapour. Lasertran (trademark of Rohm & Haas) grade is especially free of absorption and inclusions and is used particularly for CO2 laser optics at 10.6 micrometres wavelength. It is thus a very important IR material. In daily life, it can be found as the entrance optic in the new range of "in-ear" clinical thermometers and can be just seen as a small yellow window. Zinc selenide can slowly react with atmospheric moisture if poorly polished, but this is not generally a serious problem. Except where optics are use in spectroscopy or at the brewster angle, antireflection or beamsplitting coatings are generally employed.
- Fragile, breaks easily.
Chemistry
ZnSe reacts with acids to form toxic hydrogen selenide gas.
It is formed by chemical vapour deposition techniques including MOVPE.
See also
References
- ^ Cr2+ excitation levels in ZnSe and ZnS, G. Grebe, G. Roussos and H.-J. Schulz, J. Phys. C: Solid State Phys. vol. 9 pp. 4511-4516 (1976) doi:10.1088/0022-3719/9/24/020
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