1. LECTURE 10.1

2. LECTURE OUTLINE Weekly Deadlines Weekly Deadlines Electronic Properties I Electronic Properties I

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

5. THE WATER ANALOGUE: CURRENT AND PRESSURE

6. THE ELECTRON PUMP

7. CONDUCTIVITY AND OHM’S LAW

8. The current that flows through a material is proportional to the Voltage (or Electrical Pressure Difference) The current that flows through a material is proportional to the Voltage (or Electrical Pressure Difference) Or: Or: I  V I  V Or: Or: I =  V I =  V Where  is called the conductivity. Where  is called the conductivity.

9. 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

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

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

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

13. 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 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 n/atom ~ 0

14. 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 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 n/atom ~ 1

15. 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! 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!

16. ELECTRICAL CONDUCTIVITY IN A METAL

17. 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. 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 the frequency of atomic collisions increases. The drift velocity decreases as temperature increases. The drift velocity decreases as temperature increases. The drift velocity decreases as the solute level increases. The drift velocity decreases as the solute level increases.

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