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

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

5. JTE = {JTE-sat} {JTE-sat} = Jdiode = {Jdiode-sat}
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:
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7. Answer:
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11. VM Ayres, ECE875, S14

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

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

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

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

16. Example:
real ^
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19. intercept
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21. Now use this 2nd Df to make a 2nd estimate for ND
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. 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

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