PN DIODES

Atif ImamNIIT UNIVERSITYB.Tech(1st Year)CSE

SEMICONDUCTOR DIODE

Theory of p-n junction .p-n junction as diode.Ideal diode.Volt-Current characteristics.Diode biasingDifferent types of Diodes.

Theory of p-n junctionWhen a p-type semiconductor material is suitably joined to n-type semiconductor the contact surface is called a p-n junction.

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Depletion region

P N

p-n junction as diode

Also called as semiconductor diode .

The left side material is a p-type semiconductor having negative acceptor ions and positevely charged holes. The right side material is n-type semiconductor having positive donor ions and free electrons .

Construction

NP

Symbol

Anode Cathode

When forward biased, a diode acts as a conductor andcurrent flows When reverse biased, a diode acts as an insulator and no

current flows.

Forward Biased Reverse Biased

IDEAL DIODE

When the diode is ON, it acts like a short circuit and

current flow

When the diode is OFF, current is zero, so it acts like an open circuit

V/I CHARACTERISTIC

S

Diode Biasing

D

RV

D

RV

Short circuit

I

Forward Biased

Reverse Biased

D

RV

D

RV

Open circuit

I = 0

Types of Diodes

• Light Emitting Diode (LED)• Avalanche Diode.• Laser Diode.• Schottky Diode.• Zener Diode.• Photo Diode.• Varicap Diode or Varactor Diode.• Rectifier Diode.

ZENER DIODE

It was named after Clarence Zener, who discovered this electrical property.

It Permits current in the forward direction as well as in the reverse direction if the voltage is larger than the breakdown voltage or “Zener knee voltage” or “Zener voltage”.

USES Zener Diode Shunt Regulator. Zener Diode as Peak Clipper. Switching operation.

USES OF ZENER DIODE1. Zener Diode Shunt Regulator

2. Meter Protection

3. Zener Diode as Peak Clipper

4. Switching operation.

Light-emitting diodes (LEDs) Emits visible light when an

electric current passes through it. LED’s are essentially pn diodes operated in

forward bias.

Benefits Of LED:• Low power

requirement.• High efficiency.• Long life.

Applications:

• Indicator lights.• LCD panel backlighting.• Fiber optic data transmission.• Remote control.

Photo Diode A type of photo detector capable of converting light into either current or

voltage. Designed to operate in reverse bias.

n- region

p+ Active AreaInsulation

Depletion region

Back Metalization

n+ Back Diffusion

FrontContact

RearContact

Incident light

Absorbtion in the depletion layer causes current to flow across the photodiode and if the diode is reverse biased considerable current flow will be induced

USES :

Used in:• CD Players.• Smoke Detectors.• Light sensors• Various medical applications, such as

detectors for computer tomography and pulse oximeters.

Tunnel Diode (Esaki Diode)

It was introduced by Leo Esaki in 1958. Heavily-doped p-n junction

Impurity concentration is 1 part in 10^3 as compared to 1 part in 10^8 in p-n junction diode

Width of the depletion layer is very small(about 100 A).

It is generally made up of Ge and GaAs.

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