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Semiconductor recycling plant case study of GaAs photovoltaic manufacturing - case study
Gallium arsenide (GaAs) is a semiconductor material that is used in a wide variety of applications ranging from circuits to solar cells. GaAs is most useful for solar cell applications in a thin film form, which can be obtained in several ways.
Thin films of GaAs can be produced using both bulk and epitaxial growth.
There are two common ways to produce GaAs using bulk growth, Liquid-Encapsulated Czochralski (LEC) growth, and Vertical Gradient Freeze (VGF) technology.
LEC growth is accomplished by melting high-purity arsenic and gallium in a high temperature vessel, and slowly cooling to produce a single crystal. The GaAs crystal produced using this method however has some impurities such as significant levels of carbon, and numerous dislocations. These impurities cause the semiconductor to be unusable for some applications.
VGF technology works by placing high purity arsenic and gallium in an enclosed quartz ampoule with a crystal of GaAs. The arsenic and gallium are melted, and then brought into contact with the GaAs crystal. When cooled slowly, a single crystal of GaAs is formed.
The most common ways of producing GaAs films are Vapour Phase Epitaxy (VPE), Metalorganic Chemical Vapour Deposition (MOCVD), and Molecular Beam Epitaxy (MBE).