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ECE 875: Electronic Devices

This lecture focuses on metal-semiconductor junctions with an emphasis on thermionic emission models and current density. Professor Virginia Ayres from Michigan State University presents key concepts including the Richardson constant, examples of thermionic current density, and models for Schottky barriers. The lecture aims to deepen understanding of semiconductor behavior in the context of thermionic emission, providing both theoretical and practical insights applicable to electrical and computer engineering.

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ECE 875: Electronic Devices

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  1. ECE 875:Electronic Devices Prof. Virginia Ayres Electrical & Computer Engineering Michigan State University ayresv@msu.edu

  2. Lecture 24, 12 Mar 14 • Chp 03: metal-semiconductor junction • Currents: • Thermionic emission model • Examples • Richardson constant(s) • Additional models VM Ayres, ECE875, S14

  3. Start: EC VM Ayres, ECE875, S14

  4. Total Thermionic Current density: JTE = J s->m + J m->s JTE = = {JTE-sat} JTE-sat = VM Ayres, ECE875, S14

  5. Metal-semiconductor thermionic current density: JTE = {JTE-sat} {JTE-sat} = Similar in form to pn junction current density: Jdiode = {Jdiode-sat} VM Ayres, ECE875, S14

  6. Example: VM Ayres, ECE875, S14

  7. Answer: VM Ayres, ECE875, S14

  8. VM Ayres, ECE875, S14

  9. VM Ayres, ECE875, S14

  10. VM Ayres, ECE875, S14

  11. VM Ayres, ECE875, S14

  12. Metal-semiconductor junction with Schottky barrier  WD: semiconductor metal -- -- -- -- ND+ ND+ ND+ ND+ ND+ ND+ ND+ ND+ WD p+n junction  WD: semiconductor p+ -- -- -- -- NA NA NA NA ND+ ND+ ND+ ND+ ND+ ND+ ND+ ND+ NA NA NA NA VM Ayres, ECE875, S14 WD

  13. Metal-semiconductor junction with Schottky barrier  WD CD semiconductor metal C-V measurement good C-V: ybi => ideal qfBn0 I-V: TE: real qfBn (also photoelectric measurement) qfBn = qfBn0 -Df -- -- -- -- ND+ ND+ ND+ ND+ ND+ ND+ ND+ ND+ WD p+n junction  WD CD: semiconductor p+ -- -- -- -- NA NA NA NA ND+ ND+ ND+ ND+ ND+ ND+ ND+ ND+ NA NA NA NA VM Ayres, ECE875, S14 WD

  14. Metal-semiconductor junction with Schottky barrier  WD CD semiconductor metal C-V measurement good -- -- -- -- ND+ ND+ ND+ ND+ ND+ ND+ ND+ ND+ WD Intercept: ybi Slope: ND VM Ayres, ECE875, S14

  15. Metal-semiconductor junction with Schottky barrier  WD CD semiconductor metal C-V measurement good C-V: ybi => ideal qfBn0 I-V: TE: real qfBn (also photoelectric measurement) qfBn = qfBn0 -Df -- -- -- -- ND+ ND+ ND+ ND+ ND+ ND+ ND+ ND+ WD Intercept: ybi Slope: ND VM Ayres, ECE875, S14

  16. Example: real ^ VM Ayres, ECE875, S14

  17. VM Ayres, ECE875, S14

  18. VM Ayres, ECE875, S14

  19. intercept VM Ayres, ECE875, S14

  20. VM Ayres, ECE875, S14

  21. Try it: Now use this 2nd Df to make a 2nd estimate for ND VM Ayres, ECE875, S14

  22. VM Ayres, ECE875, S14

  23. Lecture 24, 12 Mar 14 • Chp 03: metal-semiconductor junction • Currents: • Thermionic emission model • Examples • Richardson constant(s) • Additional models VM Ayres, ECE875, S14

  24. Richardson constant: m* = # m0 With m* = m0 = 9.1 x 10-31 kg, A* = A A = Richardson constant = 120 A/cm2 K2 VM Ayres, ECE875, S14

  25. Conductivity effective masses m*/m0 result in: “Ge-like” surface: 8 equivalent directions VM Ayres, ECE875, S14

  26. In your HW Pr. 08 (b): A* -> A** If tunnelling is present, it will significantly impact A*: p. 162 fP is probability of thermionic emission over barrier assuming the electrons have a Maxwellian distribution of energies fp is distorted from a straight percent by amount fQ, which is related to additional quantum mechanical tunneling and reflection VM Ayres, ECE875, S14

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