Atomic Number / Atomic Weight Chart / Atomic Symbol Semiconductor Materials; Gallium: Ga; atomic number 31 Germanium: Ge; atomic number 32 Silicon: Si; atomic number 14 Gallium Arsenide: GaAs; [Ga atomic number 31. As atomic number 33] Silicon Germanium: SiGe; [Si atomic number 14. Ge atomic number 32] Selenium: Se; atomic number 34 Cadmium Telluride: CdTe; [Cd atomic number 48. Te atomic number 52]  The Periodic Table of Elements is provided for education purposes only. The editor is an electrical engineer and not a chemist or scientific student. The EPA has regulations and standard regarding Lead, Pb. The US Military has additional requirements for MIL Spec parts that may need to be addressed: Environmentally preferable materials should be used to the maximum extent possible that the material meets or exceeds the operational and maintenance requirements, and promotes economically advantageous life cycle costs. The Environmental Protection Agency (EPA) lists the top seventeen hazardous materials targeted for major usage reduction. If any of these hazardous materials are required, it is recommended that it be used only when other materials cannot meet performance requirements. Some standards go on to say that; Users should select the PIN [Part Identification Number] with the least hazardous material that meets the form, fit and function requirements of their application. EPA top 17 hazardous materials & common uses; Benzene [Solvent & gas additive] Dichloromethane [Solvent] Tetrachloroethylene [Solvent] Cadmium and compounds [Batteries] Lead and compounds [Component Leads, Solder] Toluene [Solvent] Carbon Tetrachloride [Solvent] Mercury and compounds 1,1,1 - Trichloroethane Chloroform Methyl Ethyl compounds Trichloroethylene Chromium and compounds Methyl Isobutyl Ketone Xylenes Cyanide and compounds Nickel and compounds Although the list has little to do with the periodic table, the information is notable. Selenium is used as a semiconductor in electrical rectifiers and photocells. ... The basic component of the selenium rectifier is a steel or aluminum plate coated with a 1-micrometer (μm) film of nickel or bismuth, which is used as one electrical contact upon which a 50 to 60 μm layer of halogen-doped selenium is deposited; this, in turn, is covered with a film of cadmium alloy, which is used as the other electrical contact. The selenium layer is converted into polycrystalline gray (hexagonal) selenium by annealing. The metal plate configuration lends itself to stacking, which makes these rectifiers suitable for high-voltage, as well as low-voltage power supplies. They have a high (85-percent) working efficiency and are more durable and reliable than competitor rectifiers. This reliability is a factor that, in some end uses, is of more importance than the lower cost of some competitors, such as silicon rectifiers. Although they have been largely supplanted by the lower cost silicon diode, they still have niche markets in such devices as arc welders, electrostatic air cleaners, and some kinds of transformers. |