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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 25, 14 Mar 14. Chp 03: metal-semiconductor junction Currents: Richardson constant(s) Additional models Specific resistance across SB-type contact.

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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 25, 14 Mar 14 • Chp 03: metal-semiconductor junction • Currents: • Richardson constant(s) • Additional models • Specific resistance across SB-type contact VM Ayres, ECE875, S14

  3. 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

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

  5. 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

  6. Special region at interface also impacts A**: vR is is the effective recombination velocity vD is the effective diffusion velocity VM Ayres, ECE875, S14

  7. Special region at interface also impacts A**: vR is is the effective recombination velocity vD is the effective diffusion velocity 3. Jrec 4. diffusion of electrons 5. diffusion of holes VM Ayres, ECE875, S14

  8. Lecture 25, 14 Mar 14 • Chp 03: metal-semiconductor junction • Currents: • Richardson constant(s) • Additional models • Specific resistance across SB-type contacts VM Ayres, ECE875, S14

  9. All electrons have KE well above EC 1. Thermionic emission: enough KE compared with height qfBn is critical 1.5 Thermionic-field emission: enough KE to reach thinner WD critical 2. Tunnelling (WD is critical) Note: device is ON and in forward bias WD VM Ayres, ECE875, S14

  10. Current transport processes through Schottky Barriers: Transport mechanisms; - Thermionic emission - Thermionic + diffusion - Thermionic + tunnelling- Tunnelling Schottky Barrier (height, width ): Diode I-V Schottky Barrier (height, thin width): Ohmic I-V VM Ayres, ECE875, S14

  11. Current densities for 3 major transport mechanisms in forward bias are: Thermionic emission: F TE Thermionic + field emission: Field emission = tunnelling: VM Ayres, ECE875, S14

  12. E00 is the comparison of thermal energy kT to doping written as an energy. Both can influence electron energy relative to EC VM Ayres, ECE875, S14

  13. Lecture 25, 14 Mar 14 • Chp 03: metal-semiconductor junction • Currents: • Richardson constant(s) • Additional models • Specific resistance across SB-type contacts: • - TE • - FE VM Ayres, ECE875, S14

  14. Specific contact resistance RC (W cm-2)definition: 1st step 2nd step VM Ayres, ECE875, S14

  15. Note: easy dJ/dV derivatives for V-functions in red boxes. Harder but not too bad for blue box combination functions Thermionic emission: F TE Thermionic + field emission: Field emission = tunnelling: Often this approximation is good VM Ayres, ECE875, S14

  16. RC for TE model: Function of effective barrier height and temperature VM Ayres, ECE875, S14

  17. RC for TFE model: Function of effective barrier height and temperature and doping VM Ayres, ECE875, S14

  18. RC for FE model: Function of effective barrier height and temperature and doping VM Ayres, ECE875, S14

  19. Plot of the results of carrying out those derivatives: (MSM: 2 SB device) VM Ayres, ECE875, S14

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