unbiased diode, forward biased , reverse biased diode,breakdown,energy hills

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GOVERNMENT ENGINEERING COLLEGE - BHARUCH (014) SUB : ELECTRONICS DEVICES & CIRCUITS (2131006) E.C Div A Topics : The Unbiased Diode, Forward Bias, Reverse Bias, Breakdown, Energy Levels, The energy Hill, The Barrier Potential and Temperature , Reverse-Biased Diode Created by: Meghwal Dinesh S. 130140111041 Mistry Keyur R. 130140111043 Nakrani Pratik R. 130140111046

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Presentation of Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

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Page 1: Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

GOVERNMENT ENGINEERING COLLEGE - BHARUCH (014)

SUB : ELECTRONICS DEVICES & CIRCUITS (2131006)

E.C Div A

Topics :The Unbiased Diode, Forward Bias, Reverse Bias, Breakdown, Energy Levels, The energy Hill, The Barrier Potential and Temperature , Reverse-Biased Diode

Created by:

Meghwal Dinesh S.130140111041

Mistry Keyur R. 130140111043

Nakrani Pratik R. 130140111046

Page 2: Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

The Unbiased Diode

What is Diode :- A semiconductor device with two terminals, typically allowing the flow of

current in one direction only.

What is Unbiased Diode :- when we do not apply any source of energy or electricity than a

diode is said to be unbiased diode.

Page 3: Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

The Unbiased Diode FORMATION OF P-N JUNCTION

p type semiconductor

n type semiconductor

AnodeCathode

Junction

P side is called as N type is called as

HolesElectrones

MajorityMinority

Minority

Majority

Diffusion is same

Page 4: Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

If p region is connected to the positive terminal of external dc source & n region is connected to negative terminal of dc source is said to be forward biasing.

Forward bias

IfIf

Forward biasing of a diode Symbolic Representation

Page 5: Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

Operation of a Forward biased Diode

--

--

-

+

+

++

+

+

+

-

-

p n

R

Current limiting resister

V

Due to negative terminal of external souce connected to n-region so electrons are pushed towards p-side

Due to Positive terminal of external souce connected to p-region so holes are pushed towards n-side

The holes Converting into the negative ions into neutral atomes

The Electrones Converting into the Positive ions into neutral atomes

Due to this The width of deplation region will reduce

Due to reduction in the depletion region width the barrier also reduced.

Hence a large number of electrons & holes can cross the junction under the influence of externally connected DC voltage

As we can say that the flow of electrons is current so that the current produce in this position said to be forward Current

Page 6: Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

If p region is connected to the negative terminal of external dc source & n region is connected to Positive terminal of dc source is said to be reverse biasing.

Reverse bias

Reverse biasing of a diode Symbolic Representation

Ir Ir

Page 7: Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

Operation of a Reverse biased Diode

-----

+

+

++

+

+

+

-

-

p n

RCurrent limiting resister

VHoles in P region are attracted towards negative terminal of supply

Electrones in n region are attracted towards positive terminal of supply.

Due to this The width of deplation region will incresases

Due to increases in the depletion region width the barrier also increases.

Minority carrier in p-region attracted towards positive of supply.

So that few electrons are flow so the current is also tiny that current states at this position said to be reverse saturation current due to minority carrier

-----

+++++

The process of widening is not take place at longer time due to there is no steady flow of current from n-side to p-side

Page 8: Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

BreakdownThe reverse saturation current flowing in reverse biased diode is dependent only on temperature & independent on reverse applied voltage externally.The breakdown in reverse biased diode can take place due to following effects.

Avalache effect

Zener effect

BREAKDOWN

Page 9: Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

Due to large voltage velocity

of minority carriers will

increase to great exent

Therefore Kinetic energy also

increses

While traveling minority carriers will collide with stable atomes & import some of

kinetic energy To the valance

electrons present in co-valent band

Due to this additional energy these electones will break the

covalent bonds &jump into the

conduction band to free for

conduction.

Now this free electones will be

accelerated &they knockout

some more valance

electrons by means

collisions.

THIS “CHAIN REACTION” IS

CALLED as “AVALANCHE

EFFECT”

Breakdown due to Avalache effect

Page 10: Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

Due to heavy doping of p & n side

of the diode the deplation region is narrow in reverse biased condition.

Therefore electrical field which is the voltage per unit distance is very

intense across the deplation region

This intense electric field can pull some of valence electrons by breaking the covalent bonds these electrons

than become free electrons.

The large number of such electrons can constitute through diode this is called as the breakdown

due to zener effect

Break down due to Zener effect

Page 11: Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

Each electrons orbit has an energy leval associated with it. The electrons in the inner orbits are more closely bound to the nucleus to the nucleus and posses less energy.

As we move towards the valance shell, the bliding force between nucleus & electrons reduces and the electrons reduces & elctrones posses higher energy.

Energy Levals

Shell 1 Lowest energy

Energy leval increses as we move away from the nucleus

Valance orbit has highest energy leval

Page 12: Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

Energy Bands

First band

Formed by cluster of energy leval in first shell

Concept of forbidden gap:

• Forbidden gap is energy gap that separates the conduction band & Valence bands.• For any material the forbidden gap may be large, small , or even nonexistent. The

materials are classified as conductor , insulator, semiconductors based on relative widths of forbidden gap.

Page 13: Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

Energy Hill

A Kp-region n-region

Energy

Conduction band

Valence band

The Valence & Conduction bands are slightly lower energy levals

This is Due to difference in the atomic characteristics of the pentavalent(n-type) & Trivalent(p-tpye) impurity atomesMajority

carriers(Holes)

Minority carriers(electrons)

Minority carriers(Holes)

Majority carriers(electrons)

Page 14: Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

Inernal temperature of p-n junction is known as the junction temperature

Whereas the air surrounding the device is called as ambient temprerature

Barrier Potential & Temperature

For conducting Diode

Junction Temp. > Ambient Temp.

Barrier Potential 1junction temperature

So that Due to Incresed Temp. barrier potential decreases more electrons & hole pair produced . These will diffuse into deplation region to narrow it down.

The barrier potential of a silicon diode decreases at 2 mV per degree Celsius rise in junction temperature.-2mV/

Page 15: Unbiased diode, Forward biased , reverse biased diode,breakdown,energy hills

Thanks For

Watching……….

Circuit Courtesy : Circuit MakerPlatformed by :- Microsoft office 2013