LSU EE 3950 - Semiconductors (58 pages)

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Semiconductors



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Semiconductors

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Pages:
58
School:
Louisiana State University
Course:
Ee 3950 - Electronics
Electronics Documents

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Semiconductors Crystalline solid materials whose resistivities are values between those of conductors and insulators Good electrical characteristics and feasible fabrication technology are some reasons why silicon is by far the most important semiconductor material in use today Compound semiconductor materials such as gallium arsenide are used in photonic and microwave applications and germanium is used for a few special purposes Semiconductors Silicon atoms join together to form a regular three dimensional structure called a crystal lattice Pure semiconductor materials termed intrinsic semiconductors are neutral in total charge and are also a poor conductor of electricity This means they have very few charge carriers Intrinsic Semiconductor Doping Process that adds a small amounts of impurities dopants to a semiconductor so that it can be made to contain a desired number of either holes or free electrons After the doping process the materials generated are termed extrinsic semiconductors They are impure Impurities are classified as either Donor Acceptor Extrinsic Semiconductors Donor impurities donate extra electrons to the silicon lattice Antimony Arsenic and Phosphorus They have 5 electrons in their outer electron shell Four of them will be used in the covalent bonds to the neighboring silicon atoms but the fifth can be easily freed from their original atoms by thermal energy even at room temperatures N Type Semiconductor Semiconductor materials doped to contain excess free electrons are considered n type semiconductors Even though the added impurity created excess free electrons the material is still neutral in charge It has been found that in n type materials the free electron concentration is approximately equal to the donor atom doping density n N D N Type Semiconductor Extrinsic Semiconductors Acceptor impurities create a hole in the silicon lattice Boron Gallium and Indium They have 3 electrons in their outer electron shell and they are not enough to fill



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