Chapter_14

# Chapter_14 - Chapter 14 Electrical Properties 14.1 Metals...

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1 Chapter 14 Electrical Properties 14.1 Metals 14.2 Intrinsic semiconductors 14.3 Extrinsic semiconductors Chapter 14 ME 201: Materials Science, Z. Hao 1 14.4 Semiconductor devices and Microelectronics Metals - Classic Model ± Metallic bonds make free movement of valence electrons possible. ± Outer valence electrons are completely free to move between positive ion cores positive ion cores. ± Without electrical field : the motion of electrons are random and restricted. ± With electric field : electrons attain directed drift velocity. Chapter 14 ME 201: Materials Science, Z. Hao 2

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2 Metals - Ohm’s Law (1) ± Ohm’s law: the relation between electric current flow I, applied voltage V and the resistance of the wire. i = V/R i = electric current (A), V = voltage (V), R = resistance of wire ( ) Chapter 14 ME 201: Materials Science, Z. Hao 3 ± Electric resistivity: ρ = RA/l l = length, A = Cross-sectional area ± Electric Conductivity: σ = 1/ ρ ± Electrical field: E=(V 2 -V 1 )/l ± Current density: J =i/RA= σ E Metals - Ohm’s Law (2) Example: A nichrome wire must have a resistance of 120 .How long must it be (in meters) if it is 0.0015 in. in diameter? Solution: Chapter 14 ME 201: Materials Science, Z. Hao 4
Intrinsic semiconductors Silicon, Germanium N-type Extrinsic semiconductors + 3A elements P-type Extrinsic semiconductors + 5A elements Chapter 14 ME 201: Materials Science, Z. Hao 5 Electronics Intrinsic Semiconductors (1) ± Semiconductors: Conductors between good conductors and insulators. ± Intrinsic Semiconductors: Pure semiconductors and Intrinsic Semiconductors: Pure semiconductors and conductivity depends on inherent properties. ± Example: Silicon and Germanium – each atom contributes 4 valence electrons for covalent bond. ± Valence electrons are excited away from their bonding Chapter 14 ME 201: Materials Science, Z. Hao 6 position when they are excited. ± a hole behind.

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Chapter_14 - Chapter 14 Electrical Properties 14.1 Metals...

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