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Understanding Electronic Properties, Conductivity, and Ohm’s Law in Metals and Semiconductors

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skule
18 diapositives · 288 Views · Oct 13, 2014

This lecture explores the fundamentals of electronic properties, focusing on metallic conduction and Ohm's law. It examines the relationship between current, voltage, and conductivity, explaining how free electrons contribute to conductivity in metals and semiconductors. Key concepts such as drift velocity, charge carriers, and the ionization energies of Group IV elements are discussed, highlighting differences between insulators, conductors, and semiconductors. The effects of temperature and purity on metallic conductivity are also analyzed, providing a comprehensive understanding of electrical behavior in materials.

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  1. LECTURE 10.1

  2. LECTURE OUTLINE • Weekly Deadlines • Electronic Properties I

  3. ELECTRONIC PROPERTIES I • Metallic Conduction • Ohm’s law • Number of Free Electrons/Atom • Drift Velocity • Free Electron/Electron Hole Pairs • The Group IV Elements

  4. THE WATER ANALOGUE: CURRENT AND PRESSURE

  5. THE ELECTRON PUMP

  6. CONDUCTIVITY AND OHM’S LAW

  7. CONDUCTIVITY AND OHM’S LAW • The current that flows through a material is proportional to the Voltage (or Electrical Pressure Difference) • Or: • I a V • Or: • I = sV • Where s is called the conductivity.

  8. CONDUCTIVITY AND OHM’S LAW The current that flows along the wire is equal to the number of charge carriers (electrons) times their “drift velocity” times the charge on the electron Or: I = qnv

  9. CONDUCTIVITIES OF MATERIALS • For metals: • n/atom ~ 1 • For non-metals: • n/atom ~ 0 • For semiconductors: • n is small, but finite • For metals: the conductivity (s) depends on how the drift velocity varies with e.g., temperature

  10. HOW ARE FREE ELECTRONS CREATED IN A COVALENTLY BONDED SEMICONDUCTOR? • Free electron/electron hole pairs may be created by: • Light √√ • Heat √√ • Electric Field xx

  11. CREATION OF A FREE ELECTRON/ELECTRON-HOLE PAIR

  12. IONIZATION ENERGIES OF THE GROUP IV ELEMENTS I • For diamond-C, the outer-shell electrons are in the L-shell. They are so closely bound, that the ionization energy is prohibitively high: diamond-C is a prototypical, electrical insulator • n/atom ~ 0

  13. IONIZATION ENERGIES OF THE GROUP IV ELEMENTS II • For lead, the outer-shell electrons are in the P-shell. They are so loosely bound, that lead’s outer-shell electrons are free at room-temperatures: lead is a prototypical, electrical conductor • n/atom ~ 1

  14. IONIZATION ENERGIES OF THE GROUP IV ELEMENTS III • For silicon and germanium, the ionization energies are such that their electrical properties are midway between those of a “typical” insulator, and a “typical” conductor: they are elemental semiconductors!

  15. ELECTRICAL CONDUCTIVITY IN A METAL

  16. THE DRIFT VELOCITY AND THE CONDUCTIVITY OF METALS • In metals, the variation in conductivity is related to the variation in the drift velocity of the electrons. • The drift velocity decreases as the frequency of atomic collisions increases. • The drift velocity decreases as temperature increases. • The drift velocity decreases as the solute level increases.

  17. EFFECT OF “PURITY” AND TEMPERATURE ON METALLIC CONDUCTIVITIES