subject code : 3320701_______________. name of subject : basic electronic_____________ name of unit...

Subject Code : 3320701_______________ .

Name Of Subject : BASIC ELECTRONIC_____________

Name of Unit : __DIODE AND ITS APPLICATIONS_______

Topic : __P-N JUNCTION DIODE _______________

Name of Faculty : __HAREKRUSHNA AVAIYA.

Parul Institute of Engineering & Technology

The P-N junction diode: The P-N junction diode is formed by joining a

piece of P-type materials to a piece of N-type material such that the crystal structure remains continuous at the boundary.

It is very useful and basic two-terminal device of very large solid state semiconductor family.

In actual practice a P-N junction is formed by using special fabrication technics.

Figure shows P-N junction and its circuit symbol.

The terminal at the P –end is called ‘anode’ (positive)

and terminal at the N –end is called ‘cathode’(negative).

• The P-N junction diode passes a large current in one direction and almost no current in the other direction.

• Therefore such a diode can be used as a rectifier.

ANODE CATHODE

(+ VE) (- VE)

JUNCTION

P-N JUNCTION

P n

ANODE

CATHODE (+ VE)

(- VE)

CIRCUIT SYMBOL

Biasing a diode:

Biasing diode

Forward biasing Reverse biasing

Biasing a diode: Biasing means application of voltage to P-

N junction diode by connection a battery across anode and cathode.

If we connect positive terminal of battery to P type and negative terminal of battery to N-type then it is called forward biasing and if we connect positive terminal of battery to N-type and negative terminal of battery to P-type then it is called reverse biasing.

Forward biasing : P N

ID

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Depletion region

VD

shows the fighter forward biased P-N junction.

The holes are repelled from the positive terminal of the battery and move towards the junction.

Similarly electrons in N-type moves towards the function……….. Because of their acquired energy, some of the holes and the free electrons penetrate the depletion region, So potential barrier is reduced.

The width of depletion region reduces and hence more majority carriers diffuse across the junction and recombine in other region.

For each recombination of free electron and hole that occur, an electron from the positive terminal of the battery enters the N-type material.

Then it drift towards the junction. P-material near the positive terminal of

the battery, and enters the positive terminal of the battery, an electron breaks the bond in the crystal and enters the positive terminal of the battery.

For each electron that breakes its bond, a hole is created.

This hole drifts toward the junction. There is continuous current in the

external.

Reverse biasing : P N

ID

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Depletion region

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IO

Show the reverse biased P-N junction.The ho les in the P-region are attracted

towards negative terminal of the battery. The electrons in the N-region are attracted

to positive terminal of the battery. Thus the majority carriers are drawn away

from the junction.The external electric field is added to the

potential barrier field increasing the height of barrier , resulting the very low reverse current which is due to minority charge carrier .

As the current is contributed by minority charge carriers it remains almost constant and it is called as saturation current.

This saturation current is independent of reverse voltage.

With reverse voltage , the electrons on the surface of crystal move towards the positive of supply.

At high voltage these electrons will have high velocity which can dislodged valence electrons.

The newly free electrons will also move towards the positive terminal of the supply and can dislodge one more electron.