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The Essential Properties of Semiconductors and their Role in Silicon Chip Technology

This lecture delves into the crucial properties of semiconductors that underpin modern silicon chip technology. It covers fundamental aspects such as doping characteristics, electron tunneling, and the depletion zone, alongside vital thermal properties like heat capacity and thermal conductivity. The course also explores band theory, Fermi-Dirac statistics, and the differences between conductors, insulators, and semiconductors. Additionally, it discusses the implications of intrinsic and extrinsic conductivity, charge carrier dynamics, and the photoelectric effect, providing a comprehensive understanding of semiconductor behavior.

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The Essential Properties of Semiconductors and their Role in Silicon Chip Technology

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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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