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Lecture 5.0

Lecture 5.0. Properties of Semiconductors. Importance to Silicon Chips. Size of devices Doping thickness/size Depletion Zone Size Electron Tunneling dimension Chip Cooling- Device Density Heat Capacity Thermal Conductivity. Band theory of Semiconductors. Forbidden Zone – ENERGY GAP.

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Lecture 5.0

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  1. Lecture 5.0 Properties of Semiconductors

  2. Importance to Silicon Chips • Size of devices • Doping thickness/size • Depletion Zone Size • Electron Tunneling dimension • Chip Cooling- Device Density • Heat Capacity • Thermal Conductivity

  3. Band theory of Semiconductors • Forbidden Zone – ENERGY GAP Conduction Band Valence Band

  4. Silicon Band Structure - [Ne]3s23p2

  5. Fermi-Dirac Probability Distribution for electron energy, E • Probability, F(E)= • (e{[E-Ef]/kBT}+1)-1 • Ef is the • Fermi Energy

  6. Number of Occupied States Density of States Fermi-Dirac T>0

  7. Difference between Semiconductors and Insulators kBT =0.0257 eV at 298˚K

  8. Probability of electrons in Conduction Band • Lowest Energy in CB • E-Ef Eg/2 • Probability in CB • F(E)= (exp{[E-Ef]/kBT} +1)-1 ) • = (exp{Eg/2kBT} +1)-1 •  exp{-Eg/2kBT} for Eg>1 eV @ 298K kBT =0.0257 eV at 298˚K

  9. Variation of Conductivity with T =d/dT

  10. Intrinsic Conductivity of Semiconductor • Charge Carriers • Electrons • Holes • = ne e e + nh e h • # electrons = # holes •   ne e (e+ h) • ne  C exp{-Eg/2kBT} ne=2(2 m*e kBT/h2)3/2 exp(-Eg /(2kBT)) Ef=Eg/2+3/4kBT ln(m*h/m*e)

  11. Mobilities

  12. Semiconductor Photoelectric Effect • Light Absorption/Light Emission (photodetector)/(photo diode laser) • Absorption max=hc/Eg

  13. Light Emitting Diode

  14. Photodiode Laser • Color depends on band gap, Eg •  =hc/Eg Eg>3.0 transparent Pb 0.37 0.27 0.33 IR detectors

  15. Diode Laser

  16. Extrinsic Conductivity of Semiconductor • Donor Doping Acceptor Doping • n-type p-type p= 2(2 m*h kBT/h2)3/2 exp(-Ef/kBT) N=nd+ni Law of Mass Action, Nipi=ndpd or =nndn

  17. Extrinsic Conductivity of Semiconductor • Donor Doping Acceptor Doping

  18. Electron Density • Dopant Concentration effects • Electron Density • Electrical Conductivity

  19. Conductivity • Intrinsic Range • Exponential with T • Extrinsic Range • Promoted to CB •   • Decreasing ,  • Joins Intrinsic   • Majority/minority Carriers • = ne e e + nh e h

  20. Majority/minority Carriers • Conductivity • = ne e e + nh e h • n-type ne>>nh • Low number of holes due to recombination. • Law of Mass Action • Nipi=ndpd • (For p-type Nipi =nndn )

  21. Extrinsic Conductivity of Semiconductor • Donor Doping Acceptor Doping • n-type p-type Ed = -m*e e4/(8 (o)2 h2) Ef=Eg-Ed/2 Ef=Eg+Ea/2

  22. Effective Mass • Holes • Electrons

  23. Wafer Sales • Following PRIME GRADE Si wafers are all single-side polish $14.50 each for 25 wafers each $11.00 for 50 or more (we can double side polish) • 4" P<111> 3.0-6.6 ohm-cm • 4" N<100> 4.0-6.0 ohm-cm • 4" P<111> 7.0-21.6 ohm-cm • 4" P<100> 12.0-16.0 ohm-cm • 4" P<111> 3.0-5.0 ohm-cm • http://www.collegewafer.com/

  24. GaP Wafer 2" Undoped (100) $180.00 each 2" S doped (111) $180.00 each

  25. C&ENews 1/6/03

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