OUTLINE pn junctions (cont’d) Reverse bias current Reversebias breakdown Reading: Chapter 6.2. Lecture #17. Carrier Concentration Profiles: Forward Bias. Carrier Concentration Profiles: Reverse Bias. Depletion of minority carriers at edges of depletion region
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OUTLINE
pn junctions (cont’d)
Reverse bias current
Reversebias breakdown
Reading: Chapter 6.2
EE130 Lecture 17, Slide 1
EE130 Lecture 17, Slide 2
EE130 Lecture 17, Slide 3
“Depletion approximation”:
EE130 Lecture 17, Slide 4
I
Forward Current
VBR
V
R
Small leakage
Current
A
P
N
(a)
R
3.7V
IC
Zener diode
(b)
AZener diodeis designed to operate in the breakdown mode.
EE130 Lecture 17, Slide 5
EE130 Lecture 17, Slide 6
High Efield:
if VBR >> Vbi
Small Efield:
EE130 Lecture 17, Slide 7
Dominant breakdown mechanism when both sides of a junction are very heavily doped.
VA = 0:
E
c
E
v
VA < 0:
Filled States

Empty States
E
c
Typically, VBR < 5 V for Zener breakdown
E
v
EE130 Lecture 17, Slide 8
EE130 Lecture 17, Slide 9
EE130 Lecture 17, Slide 10
p+ n diode:
p n+ diode:
EE130 Lecture 17, Slide 11
Reversebias breakdown:
a critical value eCR, then large reverse current will flow.
This happens at a large negative voltage, called the “breakdown voltage”:
where N is the dopant concentration on the more lightly doped side
avalanche, if N < ~1018/cm3
tunneling, if N > ~1018/cm3
EE130 Lecture 17, Slide 12
Forwardbias current
Reversebias current
EE130 Lecture 17, Slide 13