1003. Electronics 1 Slide

7/27/2019 1003. Electronics 1 Slide

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INTRODUCTORY ELECTRONICS


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Atomic Structure

Electronic Materials

P-N Junction Diodes Bipolar Junction Transistors (BJTs)

OUTLINE


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ELECTRONICS

Is the study of the behaviour of electronsin vacuum(i.e. absence of air), fluids(i.e.

gases and liquids) and in crystals.


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THE STRUCTURE OF AN ATOM


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ENERGY BAND STRUCTURE


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ENERGY-BAND DIAGRAM

Valence

Band

Conduction

Band

Energy

Gap

Insulator

Valence

Band

Conduction

Band

Conductor

Valence

Band

ConductionBand

Energy Gap

Semiconductor


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ENERGY-BAND DIAGRAM

Valence Band

Conduction Band

Energy Gap

Electron

energy

Generation of electron-hole pairs


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SOLID STATE ELECTRONIC MATERIALS

There are three types

1. Insulators

2. Conductors

3. Semiconductors


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CLASSIFICATION OF THE MATERIALS

1. According to resistivity Resistivity is the primary parameter used to

distinguish between these materials

Insulators: Materials that have very high

resistance and oppose current

Examples of insulators: air, rubber, paper,

teflon,glass,mica etc

Conductors: Materials that have very low

resistance and pass current very easily

Examples of conductors: Iron, silver, copper,

gold, aluminum


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Semiconductors: Materials that have

properties which lie between insulators

and conductors

Examples are carbon, silicon, germanium

(elements types), Gallium Arsenide,

Silicon Carbide (compounds types)


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Temperature effects on Semiconductor Materials Conductivity of Semiconductor Material is directly

proportional to Temperature

Stated differently, Semiconductor Materials(Devices)

have Negative Temperature Coefficient of Resistance Semiconductors can therefore be controlled either to

Increase their resistance and behave more like insulator

or

Decrease their resistance and behave more like aconductor

This ability to vary semiconductors resistive property

makes it useful in electrical and electronics components


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2. According to energy gapLet us use Energy Band Diagram from

Slides 5,6 and 7 to explain.


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According to Number of Valence Electrons

Find out


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SEMICONDUCTOR

Semiconductors are a group of solids whose electricalproperties are intermediate between conductors andinsulators .

For example, the resistivity of a conductor is of the orderof 10-8m, that of an insulator is 104m and that of asemiconductor is 10-1m

BASIC SEMICONDUCTOR

CONCEPTS


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Semiconductors are group IV elements i.e.

each has four valence electrons.

They are therefore called Tetravalent

Atoms The valence electrons are shared with four

neighboring atoms in a tetrahedral

arrangement forming covalent bonds,which maintain the crystalline solid

structure.

BASIC SEMICONDUCTOR

CONCEPTS


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BASIC SEMICONDUCTOR CONCEPTS

Silicon crystalline structure with covalent bonds

Si

Si

Si Si

SiSi

Si SiSi


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BASIC SEMICONDUCTOR CONCEPTS

(Semiconductor Atoms)


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BASIC SEMICONDUCTOR

CONCEPTS


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BASIC SEMICONDUCTOR

CONCEPTSINTRINSIC SEMICONDUCTOR


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DOPING

The main reason semiconductor materials

are so useful is that their behaviour can

easily be manipulated by the addition ofimpurities, through a process called doping.

Doping is the process of adding an impurity

atom to an intrinsic semiconductor to alter

its electrical conductivity

What is the purpose of doping?

Doping produces Extrinsic Semiconductor

BASIC SEMICONDUCTOR

CONCEPTS
http://en.wikipedia.org/wiki/Doping_(Semiconductors)http://en.wikipedia.org/wiki/Doping_(Semiconductors)


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BASIC SEMICONDUCTOR

CONCEPTS Types of Extrinsic Semiconductor

N- type Semiconductor

P-type Semiconductor

N- type Semiconductor is produced by using

pentavalent atom(eg , phosphorus,

antimony, arsenic) P-type Semiconductor is produced by using

trivalent atom(eg boron, aluminium)


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BASIC SEMICONDUCTOR

CONCEPTS (N-TYPE)


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BASIC SEMICONDUCTOR

CONCEPTS(P-TYPE)


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Mobile Charge Carriers And Immobile Ions

Recall the formation of

P-Type material

The number of holes

added is equal to the

number of boron atoms When the hole move away from its parent atom, the

remaining atom becomes a negative ion.

Unlike the mobile and free moving holes, this ion cannot

take part in conduction because it is fixed in the crystallattice.

This immobile ions are shown by circled minus signs

whereas the free and mobile holes are shown by uncircled

plus signs.


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Mobile Charge Carriers And Immobile Ions

Thermally generated electrons (minority carriers in this case) are

shown by un circled minus signs.

Similarly in N-Type material, the number of free and mobile electrons

which are added equals the number of donor atoms

Again, when an electron moves away from its parent atom, it leaves

behind positive ion.

This ion being fixed in the crystal structure cannot take part in

conduction.

These immobile ions are represented by circled plus signs whereas

free and mobile electrons are represented uncircled minus signs.

The thermally generated holes (minority carriers in this case) areshown by uncircled plus signs

In the figure ( with without minority carriers) the minority carriers of both

types have been neglected.

Hence the figure does not show the small number of free electrons in

the P-type material or the small number of free holes in the N-typematerial.


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P-N JUNCTION DIODE

Formed when a pure semiconductor isdoped in such a way that one half is P-Type

and the other half is N-Type

P-n junction


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P-N JUNCTION DIODE

(THEORY)


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BIASING THE DIODE

Two methods of biasing the diodeForward Biasing

Reverse Biasing


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P-N JUNCTION

FORWARD BIAS


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P-N JUNCTION

REVERSE BIAS


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P-N JUNCTION REVERSE BIAS

As shown in the circuit diagram, the barrierwidens as

Free electrons flows towards the positive

terminal of the battery and Holes towards the negative terminal.

Under normal circumstances, no current

should flowBut practically, small amount of current flows

through the circuit


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For a high applied pd (reverse bias),abreakdown of the barrier occurs leading to

a large reverse current.

The breakdown occurs due to two effects Zener effect

Avalanche effect


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Zener effect Zener breakdown occurs when the electric

field in the depletion layer increases to thepoint where it can break covalent bonds andgenerate electron hole pairs.

Avalanche effect

This occurs when the minority carriers that

cross the depletion region under the influenceof the electric field, gain sufficient kineticenergy to be able to break covalent bonds in

atoms with which they collide


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I-V CHARACTERISTICS


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Semiconductor devices play an indispensable role inelectronics

Semiconductor devices are electronic componentsthat exploit the electronicproperties of

semiconductormaterials, principally silicon,germanium, and gallium arsenideetc.

SEMICONDUCTOR DEVICES
http://en.wikipedia.org/wiki/Electronic_componenthttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Siliconhttp://en.wikipedia.org/wiki/Germaniumhttp://en.wikipedia.org/wiki/Gallium_arsenidehttp://en.wikipedia.org/wiki/Gallium_arsenidehttp://en.wikipedia.org/wiki/Germaniumhttp://en.wikipedia.org/wiki/Siliconhttp://en.wikipedia.org/wiki/Semiconductorhttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Electronic_component


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In the early days of radio and

television, transmitting and receiving

equipment relied on vacuum tubes, but

these have been completely replaced in

the last three decades by

semiconductor devices, which includetransistors, diodes, relays integrated

circuits and other electronic

components

SEMICONDUCTOR

DEVICES


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SEMICONDUCTOR

DEVICES

Diodes Transistors Integrated circuits


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SUMMARY

*Electronics

*Energy Band Concept*Basic Semiconductor Concepts

*PN junction

*I-V characteristics*Semiconductors Devices


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THANK YOU

Documents

1003. Electronics 1 Slide