What are extrinsic semiconductors?

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Extrinsic semiconductors are partially conducting and partially insulating materials that have been chemically altered to support a non-neutral electrical charge. They are the building blocks of semiconductor devices. The production of extrinsic semiconductors follows the successful production of intrinsic semiconductors and their transformation into positive (P) or negative (N) semiconductors.


When silicon dioxide undergoes the removal of oxygen atoms, the extraction of pure silicon is possible. While in liquid form, this pure silicon readily reacts with oxygen to revert to a variation of ordinary sand. By using a special production environment, such as a vacuum or an unreacted gas, the silicon material has the potential for high purity. To produce pure silicon, undesirable residues of other elements and compounds are also separated. Silicon melts at approximately 2,577°F (approximately 1,414°C), so special equipment and technology are required to produce extrinsic semiconductors.


Pure silicon has to be doped so that it does not remain an intrinsic semiconductor permanently. Doping involves the introduction of additional controlled impurities into the intrinsic semiconductor while it is in liquid form. In the electronics industry, pure silicon that functions as an intrinsic semiconductor must be converted to an extrinsic semiconductor in order to be used. If it has solidified as an intrinsic, it must be re-melted to create an extrinsic semiconductor. Once the intrinsic semiconductor is liquid, the next step is to generate a P-type or N-type semiconductor, and with the correct dopant elements or regulated impurities, the intrinsic semiconductor becomes an extrinsic semiconductor or a doped semiconductor.


Depending on the dopant utilized, extrinsic semiconductors are either N-type or P-type. A dopant, such as a boron, can have three electrons in the atom's outer, or valence, shell to produce a P-type semiconductor. Dopants having five valence electrons, such as phosphorus, are utilized to create an N-type semiconductor. Adding boron to pure fused silicon in an unreacted environment makes it a P-type semiconductor or electron acceptor while doping intrinsic silicon with phosphorus creates an N-type semiconductor or electron donor. One boron atom per up to 10 million silicon atoms is the typical ratio of the amount of impurity in an intrinsic semiconductor.


A semiconductor plant manufactures components using various extrinsic semiconductor pairings. The two-terminal diode has a single PN junction or a P-type and N-type semiconductor. Large-scale integration chips have thousands of P-type and N-type semiconductor junctions.