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

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. A = Richardson constant = 120 A/cm2 K2
m* = # m0
With m* = m0 = 9.1 x 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. Thermionic + field emission:
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. Both can influence electron energy relative to EC
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. Thermionic + field emission:
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