MIT6_012s09_lec02

MIT6_012s09_lec02 - MIT OpenCourseWare http/ocw.mit.edu...

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MIT OpenCourseWare http://ocw.mit.edu 6.012 Microelectronic Devices and Circuits Spring 2009 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
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Lecture 2 Semiconductor Physics (I) Outline Intrinsic bond model : electrons and holes • Generation and recombination • Intrinsic semiconductor • Doping: Extrinsic semiconductor • Charge Neutrality 1 6.012 Lecture 2 Electronic Devices and Circuits - Reading Assignment: Howe and Sodini; Chapter 2. Sect. 2.1-2.3
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1. Silicon bond model: electrons and holes Si is Column IV of the periodic table: IIIA IVA VA VIA 5 6 7 8 IIB B C N O Al Si P S 13 14 15 16 Zn Ga Ge As Se Cd In Sn Sb Te 30 31 33 34 48 49 50 51 32 52 Electronic structure of silicon atom: – 10 core electrons (tightly bound) – 4 valence electrons (loosely bound, responsible for most of the chemical properties Other semiconductors: – Ge, C (diamond form) – GaAs, InP, InGaAs, InGaAsP, ZnSe, CdTe (on the average, 4 valence electrons per atom) 2 6.012 Lecture 2 Electronic Devices and Circuits -
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Silicon crystal structure 5.43 A ° A ° 2.35 A Diamond lattice: atoms tetrahedrally bonded 3sp tetrahedral bond by sharing valence electrons covalent bonding Each atom shares 8 electrons low energy situation Si atomic density : 5 x 10 22 cm -3 6.012 Lecture 2 Electronic Devices and Circuits - 3
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Simple “flattened” model of Si crystal At 0K: 4 valence electrons (– 4 q ), contributed by each ion silicon ion ( + 4 q ) two electrons in bond border of bulk silicon region All bonds are satisfied all valence electrons engaged in bonding No “free” electrons 6.012 Lecture 2 Electronic Devices and Circuits - 4
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At finite temperature + • Finite thermal energy border of bulk silicon region incomplete bond (mobile hole) • Some bonds are broken • “free” electrons – Mobile negative charge, -1.6 x 10 -19 C “free” holes free holes – Mobile positive charge, +1.6 x 10 -19 C Caution: picture is misleading!
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This note was uploaded on 09/24/2010 for the course EE 6.012 taught by Professor Charlessodini during the Spring '08 term at MIT.

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MIT6_012s09_lec02 - MIT OpenCourseWare http/ocw.mit.edu...

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