Slide điện tử từ trường lecture 2 diodes

Lecture 02Diodes 圖片來自;www.personeel.glr.nl/koster/elektro/diodes.JP... Intrinsic semiconductor silicon At very low temperature ion http://oldsite.vislab.usyd.edu.au/photonics/devices/se

Lecture 02

Diodes

圖片來自;www.personeel.glr.nl/koster/elektro/diodes.JP

• Semiconductor physics

• Diode forward characteristic

• Diode reverse characteristic

• Special diodes

• Conductor (Cu, Ag)

1 8

) (

) (

8

) (

Energy gap Energy level

One atom

Level 3 : high energy

Level 1 : low energy

Intrinsic semiconductor (silicon)

At very low temperature

ion

http://oldsite.vislab.usyd.edu.au/photonics/devices/semicdev/doping2.html

Intrinsic semiconductor at room temperature

Mass-action law:

KT G E

e BT n

n np

n p

n

i

i i

2

For silicon semi-conductor

K eV

G k

eV E

B

5

31

10 62

8

12 1

10 4

5

1

300

cm

carriers n

K T

≈

Free electrons and holes generated

by thermal ionization, so the

concentration is same

i

n p

n = =

Boltzmann’s constant Material parameter

1 drift

E n

p q J

E qn

J

E qp

J

n p

drift

n n

p p

) ( μ μ μ

E : electric field strength (V/cm)

: mobility of hole/electron (cm 2 /V-sec)

μ

For intrinsic silicon :

s V cm

s V cm

μ σ

ρ

ρ μ

nq

cm nq

A

l R

E v

≡

− Ω

≡

=

=

) (

N n

AL

Nqv J

A

I J

L

Nqv T

Nq I

2 diffusion

dx

dn qD

J

dx

dp qD

J

n n

p p

s

cm D

hole diffusion electron diffusion

The conventional current direction is the positive charge flow direction

Currents in semi-conductor = drift current + diffusion current

dx

dn qD

E nq

J

dx

dp qD

E pq

J

n n

n

p p

At room temperature ( 20 o C ) V T ≈ 25 mV

coulomb q

C T

k

q

kT V

o

kelvin joules

T

19

23

10 6

1 273

10 38

1

K C

T

mV V

K C

T

T

o o

T

o o

26 300

27

25 293

p n

n

V

D D

E nq

J

dx

dp qD

E pq

J J

J J

n n

n

p p

p n

p T

+

=

−

= +

=

μ μ

0

=

T J

E nq

J

J T = n = μ n

N-type impure semiconductor (donor)

N

n p

P-type impure semiconductor (acceptor)

Doped +3 atoms: B, Ga, In,

Majority carriers are positive charges : holes

N

n n

5 +

5 +

5 + 3

+

3 +

3

+

圖片來自; www.rvweb.fr/ /electricite/partie3_4.php

Depletion region

m

μ 5 0

≈

圖片來自; www.rvweb.fr/ /electricite/partie3_4.php

PN Junction under open-circuit

: Diffusion current : Drift current

o

n

N N V

Contact difference of potential

dp V dV

dx

dV E

dx

dp p

V

E

V D

D

dx

dp p

D

E

dx

dp qD E

pq J

dx

dn qD E

nq J

dx

dp qD E

pq J

T

T

T n

p

n n

n

p p

0

T

T

V V

n

V V

T T

T

e n n

J

e p p

p

p V

p p

V V

V

dp p

V dV

2121

2 1

2 1

2

1 1

2 1

2

0

ln )

ln (ln

2 1

ln

ln

D A T

o

T o

n

N

N V

V

p

p V

V V

n p

p

N p

2 2

0

0 0

n D p

A

W W

W qN W

qN

dx x E dx

x E

qN =

電場的散度等於體電荷密度 (volume charge density) 除以真空容電率

Gauss’s Law

dx x E

ε

) (

D n

A p

N W N

W

N

N W

W

AN qW

AN qW

(

2

V N

N q

W W

W

D A

s p

n

For silicon

m m

W

cm F

dep

s

μ μ

ε

1

~ 1

0

10 04

N W

W N N

N W

W W

N

N W W

W W

D A

D p

D A

A n

n n

A

D n

p

+

=

⇒ +

=

2 0

2 2

0

)

( 2

2 2

W N

N

N N q

V

W qN W

qN V

D A

D A

n D p

容電係數

圖片來自; www.rvweb.fr/ /electricite/partie3_4.php

PN Junction reverse bias

I I

I S − D =

dep D

A

D A

J

n D N

J

AW N

N

N

N q

q

A W qN

q q

1 1

(

2

D A

s p

n

N N

q

W W

s j

V V R

J j

A C

dV

dq C

Q R

(

N N q

A C

D A

D A s

jo j

C C

圖片來自; www.rvweb.fr/ /electricite/partie3_4.php

Minority carriers distribution in forward bias (the story about reverse saturation current)

P n T

T

L x x V

V

n p

p p

P p

L x x n

n n n

n

V V n n

n

V V

e e

p L

D q J

dx

dp qD J

e p x

p p

x

p

e p x

p

e p

p

) (

0

) (

0 0

0

2

1

) 1 (

] )

( [ )

(

) (

Total loss by recombination

= External electric field inject electrons

PN Junction under forward bias

) 1 (

) (

) 1 )(

(

2 2

=

T V V

T V V

e I I

N L

D N

L

D Aqn

I

e N

L

D N

L

D Aqn

I

s

A p

p

D n

n i

s

D n

n

A p

p i

) 1 (

) 1 (

T V V

e

n L

D q J

e

p L

D q J

po n

n n

no p

p p

) ( J p J n A

s e I

Diode’s i-v relationship

) 1

v

e I

s T

nV v

s s

I

i nV

v

e I i

2 1

2

2

1

log 3

2 ln

2 1

I

I nV

I

I nV

V V

e I

I

e I

I

T T

nV V

s

nV V

s

T T

(

) 25

( 2

1 1

mA I

Si

mA I

Si

Ge n

D D

n : Ideality factor which depending on diode’s material and physical structure

s D

D

nV V

s D

D

D D

I I

V

e I I

V

I V

T D

0 0

V V

r r

25

0

7 0

Diode Model I (ideal model )

Diode Model II (constant-Voltage Drop model )

Diode Model III (Piecewise-linear model )

Special Diodes (Zener Diode)

圖片來自; www.alibaba.com/catalog/11418809/0_5w_Series

z z

L z

R

V V

P R

V V

I I

(min) (max)

L

z z

z z

L z

R

V V

P R

V V

I I

(max) (min)

L

z z

z z

L z

R

V V

P R

V V

I I

The others Special Diodes

1 Schottky Diode

- Metal + semiconductor (unipolar)

2 Light emitting diode (LED)

• 1963 Red

• 1993 Blue

• 1996 white