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Band-gap engineering
Band-gap engineering is the process of controlling or altering the band gap of a material. This is typically done to semiconductors by controlling the composition of alloys or constructing layered materials with alternating compositions. A band gap is the range in a solid where no electron state can exist. The band gap of insulators is much larger than in semiconductors. Conductors or metals have a much smaller or nonexistent band gap than semiconductors since the valence and conduction bands overlap. Controlling the band gap allows for the creation of desirable electrical properties.
== Molecular-beam epitaxy (MBE) ==
Molecular-beam epitaxy is a technique used to construct thin epitaxial films of materials ranging from oxides to semiconductors to metals. Different beams of atoms and molecules in an ultra-high vacuum environment are shot onto a nearly atomically clean crystal, creating a layering effect. This is a type of thin-film deposition. Semiconductors are the most commonly used material due to their use in electronics. Technologies such as quantum well devices, super-lattices, and lasers are possible with MBE. Epitaxial films are useful due to their ability to be produced with electrical properties different from those of the substrate, either higher purity, or fewer defects or with a different concentration of electrically active impurities as desired.〔Arthur, John R. "Molecular Beam Epitaxy." ''Surface Science'' 500, no. 1-3 (2002): 189–217.〕 Varying the composition of the material alters the band gap due to bonding of different atoms with differing energy level gaps.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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