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P-N Junctions

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P-N Junctions. Physical aspects of pn junctions. Mathematical models ... Electrostatics in PN Junction. Charge. Density. qND -qNA. x. x. Electric Field ... – PowerPoint PPT presentation

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Title: P-N Junctions


1
P-N Junctions
Physical aspects of pn junctions
Circuit Symbol
  • Basis for other devices

V -
Mathematical models
  • Depletion capacitance
  • Breakdown characteristics

2
PHYSICAL ASPECTS OF THE PN JUNCTION
3
P-N Junctions
N-type ND
P-type NA

4
P-N Junctions
N-type ND
P-type NA

5
P-N Junctions
N-type ND
P-type NA
Depletion Layer or Region

6
P-N Junctions
N-type ND
P-type NA
Depletion Layer or Region
qND
Charge Density
-qNA

7
P-N Junctions
N-type ND
P-type NA
Depletion Layer or Region
qND
Charge Density
-qNA
Band Diagram

8
Electrostatics in PN Junction
DQ r x
qND
Charge Density
x
-qNA
9
Electrostatics in PN Junction
DQ r x
qND
Charge Density
x
-qNA
Gauss' Law in 1 Dimension Electric Field
DQ / e
Electric Field
x
10
Electrostatics in PN Junction
DQ r x
qND
Charge Density
x
-qNA
Gauss' Law in 1 Dimension Electric Field
DQ / e
Electric Field
x
Vbi Built in Voltage
Electron Potential
x
11
Why is this the Equilibrium Condition?
Vbi built-in voltage
kT ln ( )
NAND
ni2
12
Why is this the Equilibrium Condition?
Vbi built-in voltage
kT ln ( )
NAND
ni2
Too much Vbi
Too little Vbi
13
P-N Junctions --- Diodes
N-type ND
P-type NA
First-Principles Model
14
P-N Junctions --- Diodes
N-type ND
P-type NA
First-Principles Model
15
P-N Junctions --- Diodes
N-type ND
P-type NA
First-Principles Model
16
P-N Junctions --- Diodes
N-type ND
P-type NA
First-Principles Model
17
Applying Voltage to a Diode
Forward Bias
FN
- V
FP
Forward Bias
18
Applying Voltage to a Diode
Forward Bias
FP
FN
- V
V -
FN
FP
Reverse Bias
19
Capacitance in pn Junctions
20
Capacitance in pn Junctions
21
Capacitance in pn Junctions
4.5
4
3.5
Cj0
3
2.5
Capacitance (fF)
2
1.5
1
0.5
0
-3
-2.5
-2
-1.5
-1
-0.5
0
0.5
Diode voltage (V)
22
Breakdown Voltage
23
Breakdown Voltage
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