What is an avalanche diode?
An avalanche diode is a special type of semiconductor device designed to operate in a reverse breakdown region. Avalanche diodes are generally made from silicon or other semiconductor materials.
Symbol of Avalanche Diode
The symbol of the Avalanche diode is the same as that of the Zener diode.
Working of Avalanche diode
The Avalanche diode allows electric current in the reverse direction when the reverse bias voltage exceeds the breakdown voltage. The point or voltage at which electric current increases suddenly is called the breakdown voltage. When the reverse bias voltage applied to the avalanche diode exceeds the breakdown voltage, a junction breakdown occurs. This junction breakdown is called avalanche breakdown.
When the reverse bias voltage is applied to the avalanche diode, the free electrons (majority carriers) in the n-type semiconductor and the holes (majority carriers) in the p-type semiconductor are moved away from the junction. As a result, the width of the depletion region increases.
When the reverse voltage applied to the avalanche diode continuously increases, at some point the junction breakdown or avalanche breakdown occurs. At this point, a small increase in voltage will suddenly increase the electric current. This sudden increase of electric current may permanently destroy the normal p-n junction diode. The breakdown voltage of the avalanche diode depends on the doping density. Increasing the doping density will decrease the breakdown voltage of the avalanche diode.
What is Avalanche Breakdown Voltage?
Once we increase the reverse bias voltage across a P-N junction, the reverse saturation current remains constant up to a certain point. If further increase this reverse bias voltage it will break down the junction i.e. electrical breakdown and the reverse current rises sharply to a high value. This critical value of reverse bias voltage at which reverse current rises unexpectedly and Avalanche breakdown occurs is known as the avalanche breakdown voltage. Typically avalanche breakdown occurs at a breakdown voltage of more than 6 V.
Difference Between Zener Breakdown and Avalanche Breakdown.
- Zener has a narrower depletion region, while Avalanche has a wider depletion region.
- Zener Breakdown occurs in a heavily doped P-N junction diode, While Avalanche Breakdown occurs in a lightly doped P-N junction diode.
- In the Zener diode, Breakdown occurs at a breakdown voltage of less than 4 V. while in the Avalanche diode, Breakdown occurs at a breakdown voltage of more than 6 V.
- The temperature coefficient is negative in the Zener diode, while in the Avalanche diode, the temperature coefficient is positive.
Use of Avalanche Diode
- Avalanche diodes are used as white noise generators.
- Avalanche diodes are used in protecting circuits.
Types of Diodes
- Zener diode
- Avalanche diode
- Light Emitting Diode
- Laser diode
- Tunnel diode
- Schottky diode
- Varactor diode
- P-N junction diode
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