e4510lecture-7 - J.W. Morris, Jr. University of California,...

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Unformatted text preview: J.W. Morris, Jr. University of California, Berkeley Engineering 45 Spring, 2010 J.W. Morris, Jr. University of California, Berkeley Engineering 45 Spring, 2010 Defects in Crystals Imperfections are present in all real crystals Often, they are added to control properties Materials engineering is largely defect engineering Classify defects by dimension Point defects: solute atoms (strength, conductivity) Line defects: dislocations (plastic deformation) Surface defects: external surface (crystal shape) Volume defects: voids, inclusions (fracture) J.W. Morris, Jr. University of California, Berkeley Engineering 45 Spring, 2010 Intrinsic Point Defects Vacancies- missing lattice atoms Always present at some concentration Permits atom motion (diffusion) through lattice Interstitialcies- lattice atoms in interstitial sites High energy defects, uncommon nin most solids vacancy interstitialcy J.W. Morris, Jr. University of California, Berkeley Engineering 45 Spring, 2010 Extrinsic Point Defects (solutes, impurities) Substitutional solutes Ex.: electrical defects in semiconductors control conductivity Interstitial solutes Ex.: carbon in steel strengthens by distorting structure J.W. Morris, Jr. University of California, Berkeley Engineering 45 Spring, 2010 Substitutional Solutes: Electrical Defects in Semiconductors Solutes can control the number and type of carriers in Si P (z = 5) introduces an electron in an excited state Electron can be liberated to conduct electricity Donor solutes create n-type extrinsic semiconductors B (z = 3) leaves a hole in a bonding state Hole can accept an electron to create a mobile positive charge Acceptor solutes create p-type extrinsic semiconductors Si Si Si Si Si Si Si Si Si B Si Si Si Si P e J.W. Morris, Jr....
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This note was uploaded on 02/09/2010 for the course ENGIN 45 taught by Professor Devine during the Spring '07 term at University of California, Berkeley.

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e4510lecture-7 - J.W. Morris, Jr. University of California,...

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