SEMICONDUCTORDIODE

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DIODE SYMBOL

Presented By:

Ansari Mohammed Maviya 01Saqib Ghatte 06Burhanuddin Kachwala 32Shubham Mayekar 18

1. Introduction to Diode - Ansari Mohd. Maviya

P-N Junction and its formationFormation of Depletion LayerExternal Biasing of P-N JunctionV-I Characteristics of P-N Junction

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The cathode of a diode is represented by the silver strip at the corner of the diode.

Diode

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P N

A K+++

++++

++++

+ ++++

++++

---

----

----

- ----

----

• P side has high concentration of holes.• N side has high concentration of electrons.• Electrons from N sides diffuse over to P

• Holes from P diffuse over to NThis Process is known as Diffusion.

P-N Junction DiodeElectronsHolesAtoms with holes

Atoms with electrons

P N

A K+++

++++

++++

+ ----

----

----

----

----

+++

++++

+

Depletion Region

• Positive immobile ions accumulate near junction on N side• Negative immobile ions accumulate on P side

Depletion Layer

External Biasing

+ -

P NForward BiasReverse Bias

----

----

+++

++++

+

Depletion Layer is very small

Depletion Layer is very large

Current does not flows inside the circuit.

0.6

Knee Voltage of Si

Breakdown Voltage

V-I Characteristics of P&N junction Diode

IF

IR

vFvR

Light Emitting Diode (LED)Zener Diode

2. Types of Diode - Saqib Ghatte

Light Emitting Diode (LED)

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LED: Symbol:

• Light Emitting Diode (LED) is a special type of diode emitting visible light when forward biased. These diodes are not made from silicon or germanium because they are heat producing materials and are not good in emitting light radiations.

LED Circuit

• A Zener Diode is a special type of properly doped crystal diode which is designed to operate in the reverse breakdown region.

2. Zener Diode

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Zener Diode: Symbol:

Biasing of Zener Diode

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+ -

• Anode is connected to the positive terminal of battery.• Cathode is connected to the negative terminal of battery.• Anode is connected to the negative terminal of battery.• Cathode is connected to the positive terminal of battery.

Zener BreakdownAvalanche BreakdownComparison between Zener and Avalanche Breakdown

3. Zener And Avalanche Breakdowns &Their Comparisions

- Burhanuddin Kachwala

Breakdown In A Diode There are two types of diodes

Zener Breakdown Avalanche Breakdown

Zener Breakdown• When the P and N regions are heavily doped,direct rupture of covalent

bonds takes place because of the strong electric fields, at the junction of PN diode. The new electron-hole paires so created increase the reverse current in a reverse biased PN diode. The increase in current takes place at a constant value of reverse bias typically nelow 6 v for heavily doped diodes. As as result of heavy doping of P and N regions, the depletion region width becomes very small and for an applied voltage of 6 V or less, the field across the depletion region becomes very high, of the order of 10 V/m, making conditions suitable for Zener breakdown. For lightly doped diodes, Zener breakdown voltage becomes high and breakdown is then predominantly by Avalanche multiplication. Though Zener breakdown occurs for lower breakdown voltage and Avalanche breakdown occurs for higher breakdown voltage such diodes are normally calls Zener diodes.Zeners are commercially available with breakdown voltages

of 1.8 V to 200 V with specified tolerance from1% to 20 %

Avalanche BreakdownDuring reverse biased condition, in the case of less heavily doped PN junction, Minority carries flowing across a junction acquire a kinetic energy which increase with the increase in reverse voltage. At sufficiently high reverse voltage (>5V) the K.E of minority carries become so large that they knock out electron from the covalent bond of the S/C material. As a result of collision the liberated electron in-turn liberated more electrons and the current becomes very large in the junction leading to the breakdown of crystal in structure itself. This phenomena is called the avalanche breakdown. It occurs in lightly doped junction.

It produce wide depletion layer.With increase in temperature avalanche breakdown voltage increases.Avalanche diode have positive temperature coefficient .

Comparison Between Zener & Avalanche Breakdown

ZENER BREAKDOWN AVALANCHE BREAKDOWN

1.This occurs at junctions which being heavily doped have narrow depletion layers 2. This breakdown voltage sets a very strong electric field across this narrow layer. 3. Here electric field is very strong to rupture the covalent bonds thereby generating electron hole pairs. So even a small increase in reverse voltage is capable of producing large number of current carriers. ie why the junction has a very low resistance. This leads to Zener breakdown.

1. This occurs at junctions which being lightly doped have wide depletion layers. 2. Here electric field is not strong enough to produce Zener breakdown. 3. Her minority carriers collide with semi conductor atoms in the depletion region, which breaks the covalent bonds and electron-hole pairs are generated. Newly generated charge carriers are accelerated by the electric field which results in more collision and generates avalanche of charge carriers. This results in avalanche breakdown.

Radio DemodulationPower ConversionTemperature MeasurementVoltage Protection

4. Applications of Diode-r - Shubham Mayekar

Radio Demodulation

It looks like this !!!!!!!!• The first use for the diode was the demodulation of amplitude modulated radio broadcasts.

• The history of this discovery is treated in depth in the radio article.

• In summary, an AM signal consists of alternating positive and negative peaks of a radio carrier wave, whose amplitude or envelope is proportional to the original audio signal.

• The diode rectifies the AM radio frequency signal, leaving only the positive peaks of the carrier wave.

• The audio is then extracted from the rectified carrier wave using a simple filter and fed into an audio amplifier or transducer , which generates sound waves. 

Power Conversion• Rectifiers are constructed from

diodes, where they are used to convert alternating current (AC) electricity into direct current (DC).

• Automotive alternators are a common example, where the diode, which rectifies the AC into DC, provides better performance than the commutator or earlier, dynamo.

• Similarly, diodes are also used in Cockcroft–Walton voltage multipliers to convert AC into higher DC voltages

It looks like this!!!!

Temperature Measurement• A diode can be used as a temperature

measuring device, since the forward voltage drop across the diode depends on temperature, as in a silicon band gap temperature sensor.

• From the Shockley ideal diode equation given above, it appears the voltage has a positive temperature coefficient but depends on doping concentration and operating temperature .

• The temperature coefficient can be negative as in typical thermostats or positive for temperature sense diodes down to about 20 Kelvin's.

• Typically, silicon diodes have approximately −2 mV/˚C temperature coefficient at room temperature.

It looks like this!!!!!!

Voltage Protection• Diodes are frequently used to conduct

damaging high voltages away from sensitive electronic devices.

• They are usually reverse-biased (non-conducting) under normal circumstances. When the voltage rises above the normal range, the diodes become forward-biased (conducting).

• For example, diodes are used in (stepper motor and bridge) motor controller and relay circuits to de-energize coils rapidly without the damaging voltage spikes that would otherwise occur.

• Many integrated circuits also incorporate diodes on the connection pins to prevent external voltages from damaging their sensinsitive transistors.

• Specialized diodes are used to protect from over-voltages at higher power

Its looks like this!!!!!!!!!

Introduction to Diode P-N Junction and its formation Formation of Depletion Layer External Biasing of P-N Junction V-I Characteristics of P-N Junction

Types of Diode Light Emitting Diode (LED) Zener Diode

Summary

Breakdowns and Their Comparison Zener Breakdown Avalanche Breakdown Comparison between both

Applications of Diode Radio Demodulation Power Conversion Temperature Measurement Voltage Protection

Questions?

Books TechMax Pulications Vision Pulication VBD Pulications

World Wide Web www.edurite.com www.wikipedia.org www.physicsforums.com www.diode.com www.thinkquest.org

References

Presentations Analog Electronics Tutorial Series:

DIODES - Kristin Ackerson Basic Laws of Electric Circuits Diodes

Thank You