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ECE 875: Electronic Devices

ECE 875: Electronic Devices. Prof. Virginia Ayres Electrical & Computer Engineering Michigan State University ayresv@msu.edu. Lecture 24, 12 Mar 14. Chp 03: metal-semiconductor junction Currents: Thermionic emission model Examples Richardson constant(s) Additional models.

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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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