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PN Junction / DIODE

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AGENDA

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SEMICONDUCTORPure siliciumP material boron dopedN material stibium dopedP material and N materialPN junctionPN junction layer 0V7PN junction characteristic

DIODE characteristicDIODE DC and ac resistanceDIODE load lineDIODE flipped resistorlineDIODE DC resistanceDIODE ac resistance

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Semiconductor, pure silicium

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Pure siliciumPure silicium

4 electrons4 electrons

Ideal is to have 8Ideal is to have 8

So share with your So share with your neighbourneighbour

Co-valence boundingCo-valence bounding

Electrical neutralElectrical neutral

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Semiconductor, pure silicium

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Pure siliciumPure silicium

4 electrons4 electrons

Ideal is to have 8Ideal is to have 8

So share with your neighbourSo share with your neighbour

Co-valence boundingCo-valence bounding

Electrical neutralElectrical neutral

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Semiconductor, P material boron doped

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P material = silicium P material = silicium (+4)(+4)

boron (+3) dopedboron (+3) doped

Boron misses Boron misses

1 positvie charge (positon) 1 positvie charge (positon) & &

1 negative charge 1 negative charge (electron)(electron)

Co-valence boundingCo-valence bounding

Electrical neutralElectrical neutral

P material misses one P material misses one electron, or has a place electron, or has a place for one electron, for one electron,

this is called a free this is called a free holehole

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Semiconductor, N material stibium doped

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N material = silicium N material = silicium (+4)(+4)

stibium (+5) dopedstibium (+5) doped

Stibium has got extra Stibium has got extra

1 positive charge (positon) 1 positive charge (positon) & &

1 negative charge 1 negative charge (electron)(electron)

Co-valence boundingCo-valence bounding

Electrical neutralElectrical neutral

N material has got one N material has got one extra electron out of the extra electron out of the bounding, bounding,

this is called a free this is called a free electronelectron

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P material and N material

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N material N material

= =

Free Free electronselectrons

P material P material = =

Free holesFree holes

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PN junction

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Anode = P=materialAnode = P=material

Kathode = N materialKathode = N material

KNAP = handsomeKNAP = handsome

K = NegativeK = Negative

A = PositiveA = Positive

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PN junction, depletion layer 0V7

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Depletion layer Depletion layer

can be made can be made

WiderWider by by

external reverse voltageexternal reverse voltage

SmallerSmaller by by

External froward voltageExternal froward voltage

Depletion layer; Uth = Depletion layer; Uth = 0V70V7

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PN junction, characteristic

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ForwardForward

Depletion layer is Depletion layer is gonegone

Ud > 0V7Ud > 0V7

Current can flowCurrent can flow

ReverseReverse

Depletion layer is widerDepletion layer is wider

Ud < 0V0Ud < 0V0

Current can NOT flowCurrent can NOT flow

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Diode, characteristic

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aa Diode Diode

Is aIs a

one one way way

streetstreet

forfor

currentcurrent

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Diode, characteristic

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AssumptionAssumption

TresholdTreshold

Voltage Voltage

for siliciumfor silicium

Ud = 0V7Ud = 0V7

for for germaniumgermanium

Ud = 0V2Ud = 0V2

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Diode, characteristic

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WhereWhere

id = diode currentid = diode current

Vd= diode voltageVd= diode voltage

KT/q = 26 mVKT/q = 26 mV

Iss = leakage current Iss = leakage current (1uA)(1uA)

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Diode, DC and ac resistance

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Diode, Load line

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How to calculate the exact value of vd and id;How to calculate the exact value of vd and id;

Graphical; use load line, indicates the load of the Graphical; use load line, indicates the load of the diodediode

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Diode, Load line

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For shureFor shure

id = ir = iid = ir = i

For shureFor shure

vs = vd + vs = vd + vrvr

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Diode, Load line

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For shureFor shure For shureFor shure

id = ir = iid = ir = i vs = vd + vrvs = vd + vr

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Diode, Flipped resistor line

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Flip the resistor line and push the Flip the resistor line and push the twotwo

curves horizontally to fit; curves horizontally to fit; vs = vd + vs = vd + vrvr

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Diode, Load line

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The flippedThe flipped

resistor resistor lineline

is called is called

LOAD-LOAD-LINELINE

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Diode, DC resistance

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For DC resistance use For DC resistance use thethe

load line methodload line method

For large voltagesFor large voltages

normally normally Vd= 0V7Vd= 0V7 is is usedused

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Diode, ac resistance

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Differentiating givesDifferentiating gives

Rd = Rd = ΔΔvd/vd/ΔΔid = 26 mV / id = 26 mV / IdId

Where kT/q = 26 mVWhere kT/q = 26 mV