Zinc selenide (ZnSe) is a light-yellow, solid compound comprising zinc (Zn) and selenium (Se). It is an intrinsic semiconductor with a band gap of about 2.70 eV at 25 °C (77 °F). ZnSe rarely occurs in nature, and is found in the mineral that was named after Hans Stille called “stilleite.”
Properties: ZnSe can be made in both hexagonal (wurtzite) and cubic (zincblende) crystal structure.
It is a wide-bandgap semiconductor of the II-VI semiconductor group (since zinc and selenium belong to the 12th and 16th groups of the periodic table, respectively). The material can be doped n-type doping with, for instance, halogen elements. P-type doping is more difficult, but can be achieved by introducing gallium.
ZnSe is used to form II-VI light-emitting diodes and diode lasers. It emits blue light.
ZnSe doped with chromium (ZnSe:Cr) has been used as an infrared laser gain medium emitting at about 2.4 µm.
It is used as an infrared optical material with a remarkably wide transmission wavelength range (0.45 µm to 21.5 µm). The refractive index is about 2.67 at 550 nm (green), and about 2.40 at 10.6 µm (LWIR). Similar to zinc sulfide, ZnSe is produced as microcrystalline sheets by synthesis from hydrogen selenide gas and zinc vapour. When free of absorption and inclusions it is ideally suited for CO2 laser optics at 10.6 µm 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, 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 used in spectroscopy or at the Brewster angle, antireflection or beamsplitting optical coatings are generally employed.
ZnSe activated with tellurium (ZnSe(Te)) is a scintillator with emission peak at 640 nm, suitable for matching with photodiodes. It is used in x-ray and gamma ray detectors. ZnSe scintillators are significantly different from the ZnS ones.
Zinc selenide (ZnSe) is listed in the Navy Handbook, along with Zinc Sulfide:
‘Electronic Warfare & Radar Systems Engineering Handbook’ issued by the Department of the Navy USA, the Naval Air Warfare Center Weapons Division. This manual is said to be UNCLASSIFIED and “approved for public release.”
The radiation emitted or reflected from the targets and backgrounds must pass through the intervening atmosphere before reaching the detection system. The radiation is absorbed and re-emitted by molecular constituents of the atmosphere and scattered into and out of the path by various aerosol components.
Figure 11 reveals the presence of atmospheric windows, i.e. regions of reduced atmospheric attenuation. IR (infrared) detection systems are designed to operate in these windows.
ELECTRO-OPTICAL COMPONENTS AND SENSORS
Windows / Domes / Lens Materials
For most applications of EO (electro-optical) systems in EW, the detection system is protected from the environment by a window or dome of optically transmissive material.
Transmission bands of representative window or lens materials are shown in Figure 14.
Figure 14. Transmission of Selected Window /Lens Materials
Lithium Floride, Magnesium Floride, Calcium Floride, Fused Quartz, Sapphire (Aluminum Oxide), Barium Floride, Magnesium Oxide, Zinc Sulfide, Zinc Selenide, Cadmium Telluride, Silicon, Germanium.