Session 6 Semiconductor devices • To know the semiconductors fundamentals – Intrinsic semiconductors

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  • Session 6

    Semiconductor devices fundamentals

    Electronic Components and Circuits

    Isabel Pérez

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

  • Semiconductor Materials and

    Diodes SKILLS

    • 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

    GAP Eo

    BC

    E

    Semiconductor

    BV

    BV BV

    UC3M 2010 3ECC - Session 6

  • Basic Semiconductor Concepts

    Intrinsic semiconductor. Electron -hole pair

    ni 2(T)=n·p n=p (intrinsic) [ ]hee pnq µµρσ ⋅+⋅== /1 [ ]hee pnq µµρσ ⋅+⋅== /1

    1,1eV Eo

    BC

    E

    Semiconductor

    1,1eV Eo

    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/cm 2])

    dx

    dp Dq

    dx

    dn DqJJJ 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- ni 2(T) = n·p

    n > p (n-type)

    UC3M 2010 7

    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+

    ni 2(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

    KT V t =

    Reverse

    Breakdown Vγγγγ = 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

    id A 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

  • 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 20 0

    D OFF

    V2(t)>0 V2(t)

  • Diode Equivalent Circuits

    1ª Approximation: Ideal Diode

    id Equivalent Circuit

    id

    Equivalent

    Circuit

    A C

    2ª Approximation 3ª Approximation

    id

    Equivalent

    Circuit

    A C rd

    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

  • Rectifier Circuits

    t[ms]

    v2(t)

    V2p f = 50Hz

    T = 20ms

    Secondary winding voltgage

    -V2p

    10 20 0

    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 20 0

    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 waveform v

    vi(t)

    UC3M 2010 17ECC - Session 6

    Vo = Vi

    D OFF

    i

    t

    Vγγγγ

    vo(t)

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