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Presentation on: ELECTROMAGNETISM

Topic: SEMICONDUCTORS

Presented to: SIR.TARIQ BHATTI

Program: BsIT-3rd Department of Computer ScienceBZU , Multan

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Group Members

>MOHAMMAD IMRAN KHAN 07-37

>TAHA KHAN 07-06

>BEENISH JAHANGIR 07-04

>TAYYABA JAHANGIR 07-33

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MOHAMMAD IMRAN KHANRoll#07-37

>SEMICONDUCTOR

>SILICON CRYSTALS

>TYPES OF SEMICONDUCTOR

>INTRINSIC SEMICONDUCTOR

>EXTRINSIC SEMICONDUCTOR

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SemiconductorsMaterials that are

neither conductor nor insulator.

Element with 4 valance electrons is the best semiconductor.

They contains free electrons.

Element with electrical properties between those of conductors and insulators.

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Difference between semiconductor and conductor is because of the existence of holes, present in semiconductors.

For example; GermaniumSilicon

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Silicon crystalsAs an insulator:

Perfect insulator at 25°C8 valance electrons, covalently bonded with

the neighboring atoms.

As a conductor:act as conductor at ambient temperature

(above -273°C) An electron gains energy, creating a vacancy

in valence shell (hole), and move to bigger orbit. Hence, become a free electron.

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Recombination:Merging of free electron and a hole.

Lifetime:Amount of time for the creation and disappearance of free electron

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Intrinsic semiconductor

Pure semiconductors.Because of thermal

energy, equal numbers of electrons & holes are present.

These are often called as ‘carriers’ because they carry charge from one part to another.

These holes & electrons move in opposite direction.

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Extrinsic semiconductor

Doped semiconductor is called extrinsic semiconductor.

Doping:A way to increase

conductivity of semiconductor.Adding impurity atoms to

intrinsic crystal to alter its conductivity.

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Increasing free electrons:Adding pantavalent atoms, e.g; Arsenic,

Antimony, PhosphorusThey are also called donar impurities,as

they donate an extra electron.

Greater the impurity added, greater will be the conductivity.

Lightly-doped semi- conductors has high resistance.

Heavily-doped semi- conductors has low resistance.

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Increasing the holes:Adding trivalent impurity, e.g;

Aluminium, Boron,Gallium.Also called acceptor atom, because

hole can accept a free electron.

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TAHA KHANRoll#07-06

>N-TYPE SEMICONDUCTOR >P-TYPE SEMICONDUCTOR

>THE UNBIASED DIODE

>PN-JUNCTION

>DEPLETION LAYER

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DEFRENCE BETWEEN INTRINSIC AND EXTRINSIC SEMICONDUCTORS

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2 types of Extrinsic semiconductors

n-Type semiconductorDoped with pantavalent impurity‘n’ stands for negativeMajority carriers are free electronsMinority carriers are the holes

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p-Type semiconductorDoped with trivalent impurity ‘p’ stands for positiveMajority carriers are holesMinority carriers are free electrons

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Unbiased Diode

Diode explains, two electrodesIt is electrically neutralAlso called junction diode or pn-

crystal

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pn-junctionBorder between p-type & n-

type semiconductors.Lead to inventions like, diode,

transistors, & integrated circuits.

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The depletion layerFree electrons diffuses from n-type to p-

type, converting the pentavalent atom in ‘n’ into positive ion and trivlent in ‘p’ into negative ion

Each pair of negative and positive ions at the junction is called Dipole

This depreted region around the junction, having no charges but only ions, is called Depletion region

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BEENISH JAHANGIRRoll#07-04

>BARRIER POTENTIAL & TEMPRATURE

>FORWARD BIAS

>REVERSE BIAS

>CURRENT IN REVERSE BIAS

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Barrier Potential

Electric field between positive and negative ions

Act as a barrier and causes no diffusion of free electrons from ‘n’ to ‘p’

The electric field between ions is equivalent to difference of potential

At 25°C the Barrier potential for; Germanium Diode is 0.3V Silicon Diode is 0.7V

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BARRIER POTENTIAL &TEMPERATURE

Junction temperature >Temperature inside the diode

Ambient temperature >Temperature outside the diode

Conducting diode>when Junction temperature is greater then Ambient temperature

>Less barrier potential at higher temperature

A barrier potential of a silicon diode decreases by 2mV for each degree celsius rise.

V/T=-2mV/°C

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Forward biasDC source across dioden-type connected to negative terminal of the

batteryp-type connected to positive terminal of the

battery

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Conduction of current is in forward direction because of flow of free electron

No current if DC voltage is less then barrier potential

Continuous current if DC voltage is greater then barrier potential

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Reverse biasn-type connected to positive terminal of

the battery

p-type connected to negative terminal of the battery

negative terminal attracts the holes in ‘p’Positive terminal attracts the free

electrons in ‘n’

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Depletion layer gets wider (because of ions created around the junction )

Greater the reverse voltage greater will be the potential

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Current in reverse biased semiconductor

Saturation current >A very small current because of minority carriers and electron- hole pair inside the depletion layer because of thermal energy..

Surface- leakage current >Caused by surface impurity and imperfection in the crystal structure.

Approximately ZERO current.

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TAYYABA JAHANGIR Roll#07-33

>ENERGY LEVELS

>ENERGY BANDS

>ENERGY BAND IN INTRINSIC SEMICONDUCTOR

>N-TYPE ENERGY BAND

>P-TYPE ENERGY BAND

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ENERGY LEVELSHigher energy in larger

orbitElectron gain energy

when lifted to larger orbit

Which has more potential after lifting

This Energy is provided by heat ,light and voltage

Falling electron radiate light

Electron lose energy in form of heat ,light, radiation when falls to lower orbit

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ENERGY BANDSElectron of an isolated silcon atom are

bound to the neucleus having distinct energy level

In a solid, energy level of these isolated atom splits into sub-levels called discrete states

These states are so close that they appear as a continuous energy band

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FORBIDDEN GAPA range of energy states

between two consective permissible energy bands which cannot be occupied by electron

VALANCE BANDThe energy band in the

outer most shell of an atom occupying free electron

It is either completely or partially filled but never empty

Conduction is because of movement of holes

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CONDUCTION BANDAbove the valance bandElectron move freely May be empty or partially filled Conduction is because of movement of

free electronBands below valance band take no part in

conduction process because they are completely filled

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ENERGY BAND IN INTRINSIC SEMICONDUCTOR

Partially filled conduction & valance band

A narrow forbidden gap of order 1eV between conduction band & valance band

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N-TYPE ENERGY BAND

P-TYPE ENERGY BAND

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COMPARISON