Semiconductors are materials that conduct electricity, but not particularly well. The very term “semiconductor” literally means “half-conductive object.” Different types of semiconductors conduct electricity in different ways. When combined, they create devices that are capable of fine control over the flow of electricity. Semiconductors are integral to all electronic devices from radios to GPS systems. There are not only many types of semiconductors, there are even many types of types. There are several different schemes under which semiconductors are classified.
Elemental and Compound
One method of classification is into elemental and compound semiconductors. Elemental semiconductors are semiconductors that are made out of a single element. These are most often made of germanium and silicon. Of these two, silicon is much more widely used. Compound semiconductors are made out of two element compounds. These include indium and antimony, indium and arsenic, gallium and phosphorus, gallium and antimony, gallium and arsenic, silicon and carbon and gallium and nitrogen.
Intrinsic and Extrinsic
Another classification scheme has semiconductors divided into intrinsic and extrinsic types. Intrinsic semiconductors are chemically pure. They contain nothing but semiconductive material. They are natural semiconductors. Extrinsic semiconductors have certain impurities added to them. This addition of impurities, called “doping,” alters the behavior of the semiconductors. These improved semiconductors are the type that is used in the electronics industry.
N-Type and P-Type
Within the category of “extrinsic semiconductor” there exist two other types. N-type semiconductors have elements such as antimony, arsenic or phosphorus impurities added. These elements have extra electrons on the outsides of their atoms that aren’t used in forming chemical bonds with the intrinsic semiconductor they are added to. These electrons give the semiconductor a negative charge. P-type semiconductors use boron, gallium or aluminum as an impurity. These elements don’t have quite enough electrons on the outsides of their atoms, and can’t form proper bonds, leaving the semiconductor with a positive charge.
Semiconductors are also classified by what sort of crystal lattice the atoms of the semiconductor grow in. Silicon and germanium, the two most common semiconductors, grow in a diamond lattice, where every atom is bonded with four others to form a tetrahedron shape. Semiconductors can also form in several different hexagonal crystal lattices. To ensure that semiconductors grow in the specific lattice that they want, engineers dip a small “seed crystal” into molten semiconductor material, causing it to copy the crystal's pattern as it cools and crystallizes.
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