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#  P-N Junction Diodes  How do they work? (postponing the math) - PowerPoint PPT Presentation

 P-N Junction Diodes  How do they work? (postponing the math). Chap. 5.2. p-n Junction Diode. p -Type Material. n -Type Material. p-n Junction. p-n Junction Diode. p -Type Material. n -Type Material. p-n Junction. p -Type Material. n -Type Material. p-n Junction.

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P-N Junction Diodes How do they work?(postponing the math)

Chap. 5.2

p-Type Material

n-Type Material

p-n Junction

p-Type Material

n-Type Material

• p-n Junction

p-Type Material

n-Type Material

p-n Junction

• A p-n junction diode is made by forming a p-type region of material directly next to a n-type region.

p-Type Material

n-Type Material

• p-n Junction

ND - NA

ND

x

NA

p-n Junction

EC

EC

EF

Ei

Ei

EF

EV

EV

n-Type Material

• In regions far away from the “junction” the band diagram

p-Type Material

EC

EC

EF

Ei

Ei

EF

EV

EV

n-Type Material

• But when the device has no external applied forces, no current can flow. Thus, the Fermi-level must be flat!

• We can then fill in the junction region of the band diagram as:

p-Type Material

EC

EC

EF

Ei

Ei

EF

EV

EV

n-Type Material

• But when the device has no external applied forces, no current can flow. Thus, the Fermi-level must be flat!

• We can then fill in the junction region of the band diagram as:

p-Type Material

EC

EC

EF

Ei

Ei

EF

EV

EV

Electrostatic Potential

Built-in-potential

x

• Built-in-potential

p-Type Material

n-Type Material

- qVBI

• Built-in-potential

Electrostatic Potential

Built-in-potential

x

Electric Field

• Electric Field

x

• Poisson’s Equation

Charge Density

(NOT Resistivity)

Electric Field

in 1-dimension

Relative Permittivity

of Semiconductor

(r)

Permittivity of free space

• Built-in-potential

Electric Field

x

• Charge Density

Charge Density

qND

+

+

+

x

-

-

-

qNA

Energy

Potential

Electrical Field

Charge Density

n

+

-

As

B

+

h

e

M

M

Metallurgical Junction

(

)

E

x

Neutral p-region

E0

Neutral n-region

-Wp

-Wn

0

x

E

o

V

(

x

)

M

V

Space charge region

o

Wp

Wn

l

o

g

(

n

)

,

l

o

g

(

p

)

p

p

o

x

n

n

o

P

E

(

x

)

n

i

e

V

o

p

Hole Potential Energy PE (x)

o

n

o

n

p

o

x

x

=

0

r

x

n

e

t

M

Electron Potential Energy PE (x)

e

N

d

W

e

V

p

o

x

p-n Junction Principles

W

n

-

e

N

a