Session 6

Semiconductor devicesfundamentals

Electronic Components and Circuits

Isabel Pérez

www.uc3m.es/portal/page/portal/dpto_tecnologia_electronica/Personal/IsabelPerez

Semiconductor Materials and

DiodesSKILLS

• To know the semiconductors fundamentals– Intrinsic semiconductors. Electron and hole.

– Extrinsic semiconductors. Impurity atoms (donors and aceptors).

– n-type and p-type semiconductors

• To understand the p-n junction fundamentals– p-n junction equilibrium . The space charge region.– p-n junction equilibrium . The space charge region.

– p-n junction biased (forward bias and reverse bias)

• To understand the i-v characteristic of the diode

UC3M 2010 2ECC - Session 6

Semiconductor Materials

Conductor InsulatorSemiconductor

Bands Theory

Eo

BC

BV

E

Eo

BC

E

Conductor Insulator

GAPEo

BC

E

Semiconductor

BV

BVBV

UC3M 2010 3ECC - Session 6

Basic Semiconductor Concepts

Intrinsic semiconductor. Electron -hole pair

ni2(T)=n·p n=p (intrinsic) [ ]hee pnq µµρσ ⋅+⋅== /1 [ ]hee pnq µµρσ ⋅+⋅== /1

1,1eVEo

BC

E

Semiconductor

1,1eVEo

BV

UC3M 2010 4ECC - Session 6

Intrinsic Semiconductors (Si)T=0ºK (thermal equilibrium)

+4

-

-

-

-

- -

+4

-

-

-

-+4

-

-

-

-

-

Covalent bond

+4

-

-- +4

-

--+4

-

--

+4

-

-

-

- +4

-

-

-

-+4

-

-

-

-

Free

T > 0ºK

UC3M 2010 5ECC - Session 6

-

+4

-

-

-

- +4

-

-

-

-

--

+4

-

-

-

-

Covalent bond

broken+

Free

electron

(e-)

Free hole(h+)

Semiconductor Currents• DIFFUSION: If free electrons concentration is made higher in one part of the piece of Si than in

another, then the electrons will diffuse from the region of high concentration to the region of low

concentration⇒diffusion current density(Jd [A/cm2])

dx

dpDq

dx

dnDqJJJ pndpdnd ••−••=+=

• DRIFT: An electric (E [V/cm2 ) field is applied]• DRIFT: An electric (E [V/cm2 ) field is applied]

+4

-

-

-

-

--

+4

-

-

-

-+4

-

-

-

-

-

e-

+

+ -E

+

Two charge carriers:

e- and h+

UC3M 2010 6ECC - Session 6

+4

-

-- +4

-

-

-

-+4

-

-

-

-

++h+

Current

EpqEnqJJJ pnapana µµ ••+•••=+=

e- and h+

n-type: Donor impurity atoms. Example: Phosphorus(P).

Extrinsic Semiconductors

+4

-

-

-

-

- -

+4

-

-

-

-+4

-

-

-

-

- -

Free e- ni2(T) = n·p

n > p (n-type)

UC3M 20107

ECC - Session 6

+4

-

-- +5

-

--+4

-

-

-

-

-e- : mayority carriers

h+ : minority carriers

Extrinsic Semiconductors

p- type: Acceptor impurity atoms. Example: Boron (B)

+4

-

-

-

-

-

+4

-

-

-

-+4

-

-

-

-

- +

Free h+

ni2(T) = n·p

p > n (p-type)

h+ : mayority carriers

UC3M 2010 8ECC - Session 6

+4

-

-- +3

-

--+4

-

--

+h+ : mayority carriers

e- : minority carriers

+p n-p-n Junction

equilibrium

Depletion or space charge region (without free carriers)

0

+ -

0

x

Charge density (ρρρρ)

x

Electric field (E)

Potential (V)

UC3M 2010 9ECC - Session 6

x

Potential (V)

Barrier voltage ( Vγγγγ )

-+

Foward bias

+ -

Vd

)1( −= t

d

nV

v

Sd eIi

• id: Mayority carriers current

+p n-id

Reverse bias

+-

Vd

Biased p-n

Juntion

+p n-

+-

id =-Is

UC3M 2010 10ECC - Session 6

-+ • id: Minority carriers current

p n

Anode Cathode

-

id

v

Symbol

The p-n

Junction Diode

Forward

Breakdown

id

vd

-Vbreak

)1( −= t

d

nV

v

Sd eIi

+ -vd

Package

Anode Cathode

I-V CAHARACTERISTIC

q

KTV t =

Reverse

BreakdownVγγγγ = 0.7V ( Si)

vd

-Is = Reverse bias

saturation current

0.5V

UC3M 2010 11ECC - Session 6

Diodes and Applications

SKILLSSKILLS

• To know the diode basic work as a circuit

component and to know the diode models

• To understand the conduction threshold and its use in diode circuits

• To know the types of diode circuits• To know the types of diode circuits

UC3M 2010 12ECC - Session 6

Ideal Diode

idA C

Equivalent Circuit

vD

ON

OFF

A C

vd=0

id>0

A C

Equivalent Circuit

Short Circuit

A C

UC3M 2010 13ECC - Session 6

A C

id=0

vd<0

Open Circuit

A CON

A C

OFF A C

Example: Half-Wave Rectifier

t[ms]

v2(t)

V2p

10 20

f = 50Hz

T = 20ms

0

Secondary winding voltage

-V2p

vO(t)

Vop=V2P

f = 50Hz

T = 20ms

0

D ON Output waveform

V2(t) > 0

V2(t) < 0

Vo(t) = V2(t)

Transfer function

t[ms]

vO

v2

UC3M 2010 14ECC - Session 6

10 200

D OFF

V2(t)>0 V2(t)<0

V2(t) < 0

D ON

D OFF

Vo(t) = 0

0

Diode Equivalent Circuits

1ª Approximation: Ideal Diode

id Equivalent

Circuitid

Equivalent

Circuit

A C

2ª Approximation 3ª Approximation

id

Equivalent

Circuit

A Crd

vd

ON

OFF

A

<

C

vd=0

id>0

Equivalent

Circuit

vd

ON

OFF

Vγγγγ

vd=Vγγγγ

id>0

+ -Vγγγγ

Equivalent

Circuit

vd

ON

OFF

Vγγγγ

vd=Vγγγγ+rd.id

id>0

A C

+ -Vγγγγ

Equivalent

Circuit

1/rd

UC3M 2010 15ECC - Session 6

A C

id=0

vd<0

A C

id=0

vd<Vγγγγ

A C

id=0

vd<Vγγγγ

Circuit

Rectifier Circuits

t[ms]

v2(t)

V2p f = 50Hz

T = 20ms

Secondary winding voltgage

-V2p

10 200

vO(t)

Vop=V2P- Vγγγγ

f = 50Hz

T = 20ms

D ON Output waveform

V2(t) > Vγγγγ

Vo(t) = V2(t) -Vγγγγ

Transfer function

vO

2ª Approximation

UC3M 2010 16ECC - Session 6

10 200

D OFF

V2(t) < Vγγγγ

D ON

D OFF

Vo(t) = 0

Vγγγγ

t[ms] v2

V2(t) < VγγγγV2(t) > Vγγγγ

Limiter Circuits

Vγγγγ

Vo

Transfer function

Vo = Vγγγγ

D ON

Vi > Vγγγγ

Vi < Vγγγγ

Vγγγγ

Vi

D OND OFF

Pendiente =1

Output waveformv

vi(t)

UC3M 2010 17ECC - Session 6

Vo = Vi

D OFF

i

t

Vγγγγ

vo(t)