Semiconductor Diodes [Demo]

8/6/2019 Semiconductor Diodes [Demo]

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SEMICONDUCTORSEMICONDUCTOR

DIODESDIODES


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SEMICONDUCTOR DIODESSEMICONDUCTOR DIODES

IntroductionIntroduction

Ideal DiodeIdeal Diode

Semiconductor MaterialsSemiconductor Materials Extrinsic MaterialsExtrinsic Materials

Semiconductor DiodeSemiconductor Diode


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IntroductionIntroduction

Diode is theDiode is the simplestsimplestof semiconductor devices butof semiconductor devices but

plays a very vital role in electronics systems, with itsplays a very vital role in electronics systems, with its

characteristics that closely match those of acharacteristics that closely match those of a simplesimple

switch.switch.

Diode schematic symbol:Diode schematic symbol:

where: Anode (+)where: Anode (+)Cathode (Cathode (--))


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Ideal DiodeIdeal Diode

An ideal diode is a perfect conductor (shortAn ideal diode is a perfect conductor (short--circuit)circuit)

in one direction, and a perfect resistor (closein one direction, and a perfect resistor (close--circuit)circuit)

in the other.in the other.

II--V characteristic curveV characteristic curve


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Ideal DiodeIdeal Diode (continuation)(continuation)


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Semiconductor MaterialsSemiconductor Materials

ConductorConductor any material that will support aany material that will support agenerous flow of charge when a voltage source ofgenerous flow of charge when a voltage source of

limited magnitude is applied across its terminal.limited magnitude is applied across its terminal. InsulatorInsulator any material that offers a very low levelany material that offers a very low level

of conductivity under pressure from an appliedof conductivity under pressure from an appliedvoltage source.voltage source.

SemiconductorSemiconductor therefore, a material that has atherefore, a material that has aconductivity level somewhere between the extremesconductivity level somewhere between the extremesof an insulator and a conductor.of an insulator and a conductor.


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Semiconductor MaterialsSemiconductor Materials (continuation)(continuation)

Characteristics of SemiconCharacteristics of Semicon

With 4 valence eWith 4 valence e--

SiliconSilicon

GermaniumGermanium

Conductivity (Conductivity () lies between conductor and insulator) lies between conductor and insulator

Negative temperature coefficient (Negative temperature coefficient (--))

as the temperature (T) increases, the resistance (R) decreasesas the temperature (T) increases, the resistance (R) decreases


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Atomic Structure Covalent bonding Atomic Structure Covalent bonding


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Intrinsic Materials are those semiconductors thatIntrinsic Materials are those semiconductors that

have been carefully refined to reduce the impuritieshave been carefully refined to reduce the impurities

to a very low levelto a very low level essentially as pure as can beessentially as pure as can be

made available through modern technology.made available through modern technology.

Extrinsic Materials are those semiconductors thatExtrinsic Materials are those semiconductors that

have been subjected to the doping process.have been subjected to the doping process. DopingDoping -- the addition of certain impurity atoms intothe addition of certain impurity atoms into

the relatively pure semiconductor material.the relatively pure semiconductor material.


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Extrinsic MaterialsExtrinsic Materials

NN--type is created by introducing those impuritytype is created by introducing those impurity

elements that haveelements that havefivefivevalence electronsvalence electrons

(pentavalent).(pentavalent).

Pentavalent elements are those that belong to Group VAPentavalent elements are those that belong to Group VA

of the Periodic table (ie. phosphorus, antinomy, arsenic)of the Periodic table (ie. phosphorus, antinomy, arsenic)

Donor atomsDonor atoms diffused impurities withdiffused impurities withfivefivevalencevalence

electronselectrons


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Extrinsic MaterialsExtrinsic Materials (continuation)(continuation)

2D Crystalline Structure of N2D Crystalline Structure of N--typetype

Net charge: neutral# of free e- > # of holes

Minority carriers: holes

Majority carriers: freee-

At room temp, it is conductive

At 100 C, it is moreconductive

Dopants: PhosphorusArsenic

Antinomy

Bismuth


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PP--type is formed by doping a pure germanium ortype is formed by doping a pure germanium or

silicon crystal with impurity atoms havingsilicon crystal with impurity atoms havingthreethree

valence electrons (trivalent).valence electrons (trivalent).

Trivalent elements are those that belong to Group IIIA ofTrivalent elements are those that belong to Group IIIA of

the Periodic table (ie. boron, gallium, indium)the Periodic table (ie. boron, gallium, indium)

Acceptor atomsAcceptor atoms diffused impurities withdiffused impurities with threethreevalencevalence

electronselectrons


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2D Crystalline Structure ofP2D Crystalline Structure ofP--typetype

Net charge: neutral# of free e- < # of holes

Minority carriers: freee-

Majority carriers: holes

At room temp, it is conductive

Dopants: Boron

GalliumIndium


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Semiconductor DiodeSemiconductor Diode

Semiconductor diode is formed by simply bringingSemiconductor diode is formed by simply bringing

the Nthe N--type and Ptype and P--type materials together.type materials together.

The electrons and holes in the region of the junctionThe electrons and holes in the region of the junctionwill combine resulting in a lack of carriers in thewill combine resulting in a lack of carriers in the

region near the junction.region near the junction.


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Semiconductor DiodeSemiconductor Diode (continuation)(continuation)

The region of uncovered positive and negative ions is calledThe region of uncovered positive and negative ions is called

thethe depletion regiondepletion regiondue to the depletion of carriers in thisdue to the depletion of carriers in thisregion.region.

The net charge on each side of the depletion region meansThe net charge on each side of the depletion region means

that there is anthat there is an intrinsic voltagedropintrinsic voltagedrop across the junction.across the junction.


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Semiconductor DiodeSemiconductor Diode (continuation)(continuation)

BiasingBiasing application of dc voltage of specificapplication of dc voltage of specific

polarity to each terminal of the diode to acquire apolarity to each terminal of the diode to acquire a

certain operating condition.certain operating condition.

No biasNo bias

Forward biasForward bias

Reverse biasReverse bias

Semiconductor Diodes [Demo]

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