How does the Avalanche Diode works?

What is an Avalanche diode?

A reverse breakdown region-operating diode is referred to as an avalanche diode. The fundamental purpose of these diodes is to break precisely at a reverse voltage without being damaged. Once these diodes are linked in series, they can be used in high voltage, inductive, protective circuits. An avalanche diode will last a lot longer than a typical diode. Therefore, reliability can be increased by utilising these diodes in particular applications.


Semiconducting and insulating materials both experience avalanche breakdown. It is a method of multiplying electric current that enables very high currents to flow through materials or other effective insulators. Once the voltage supply is given beyond the insulating material that is sufficient to speed up free electrons once they reach atoms within the material, and then they can knock other charge carriers, this type of breakdown can also happen in solids, liquids, or gases.


These diodes are the greatest surge-suppression parts because avalanches happen quickly. An avalanche diode is used in an electric system like a valve to control and safeguard it against an excess of pressure.

Construction of Avalanche Diode:

Avalanche diodes are often constructed out of silicon or other semiconductor materials. Avalanche diodes are built similarly to Zener diodes, with the exception of the doping amount, which differs from Zener diodes. The depletion area width in this diode is quite small since zener diodes are intensively doped. This region causes the reverse breakdown to occur in this diode at lower voltages.


Avalanche diodes, on the other hand, are minimally doped. As a result, as compared to a Zener diode, the depletion layer width of an avalanche diode is quite enormous. Due to the size of the depletion region, reverse breakdown occurs in the diode at higher voltages. By carefully regulating the doping level during fabrication, the breakdown voltage of this diode is determined.

Working of Avalanche Diode:

Avalanche diodes allow current to flow in both forward and reverse biassing circumstances, unlike PN junction diodes, which can only supply current when coupled in the forward bias condition. It is typically used in situations with reverse bias. The avalanche diode behaves in the forward bias state in a manner that is comparable to that of a typical PN junction diode.

The applied voltage is known as reverse bias voltage after this diode is connected in reverse bias condition. Once the reverse voltage is greater than the reverse breakdown voltage, an avalanche diode can begin to function.

As a result, this voltage is known as the reverse bias voltage when the breakdown at the PN junction occurs. The diode therefore permits the flow of current in this circumstance. Similar to a PN junction diode, this kind of diode has two layers: the P-layer and the N-layer. While electrons predominate in the N-layer, holes are the predominant charge carriers in the P-layer.

The majority of the charge carriers will leave the PN junction once this diode receives a reverse bias voltage. The majority of charge carriers will therefore limit the flow of current as the depletion region widens. Reverse leakage current which occurs in this situation as a result of the minority charge carriers is a little amount of current that flows throughout the circuit.


When the reverse bias voltage is increased, the minority charge carriers’ ability to absorb energy improves, causing them to travel quickly. Through the collision of these charge carriers with atoms, energy will be transferred toward the valence electrons. These electrons will become free electrons after being cut off from the parent atom.


Characteristics of Avalanche Diode:

The avalanche diode’s characteristics are roughly comparable to those of the Zener diode. The minority charge carriers inside the PN junction cause the avalanche breakdown. When compared to the voltage drop inside a typical zen diode, the voltage drop that occurs within the breakdown area of these diodes is modest, making it possible to build them. The avalanche diode’s VI characteristic curve is displayed below.


The difference in current for the applied voltage to the diode is what makes up the VI properties. The Zener & Avalanche breakdown has mixed properties, as shown in the graph above. It has been noted that when a diode is linked in a reverse bias state, both breakdowns will occur.

Zener breakdown often occurs below 4V of the ‘Vz’-designated breakdown voltage. Similar to avalanche breakdown, avalanche breakdown occurs at breakdown voltages greater than 6V as stipulated by VBR.

Advantages of Avalanche Diode:

Avalanche diodes have the following advantages:

  • Avalanche diode guards the circuit against harm when the voltage or current unexpectedly rises.
  • Low doping is present in the semiconductor materials that were primarily employed to construct this diode.
  • A high current is produced by the collapse of an avalanche.
  • It is quite effective.

Disadvantages of Avalanche Diode:

Avalanche diode disadvantages include the following:

  • The output of the diode is not linear
  • The required avalanche breakdown voltage is larger than that required for Zener breakdown.
  • Poor dependability
  • The noise produced inside the diode is higher than it would be in a typical PN junction diode.

Applications for Avalanche Diode:

The following are some applications of avalanche diodes:

  • The circuit is safeguarded by an avalanche diode. The diode purposefully initiates an avalanche reaction at a predetermined voltage when the reverse bias voltage starts to increase.
  • As a result, the diode can begin conducting current without harming itself, and the tremendous power is switched to the diode’s ground terminal, away from the electrical circuits.
  • The diode is more frequently used by designers to shield a circuit from errant voltages.
  • White noise generators are made from these diodes.
  • Avalanche diodes produce RF noise; they are frequently employed in radio equipment as noise sources. They commonly serve as a source of radio frequency for antenna analyzer bridges, for instance. Microwave frequency is produced by avalanche diodes.
  • Various applications employ this diode as a single photon detector.
  • Due to the fact that it functions as a negative resistance device, this diode is utilised to detect microwave frequencies.

Some Useful Questions:

1. What is VBR?

VBR – Breakdown Voltage

The lowest voltage that results in electrical breakdown and the conductive transformation of a part of an insulator is known as the breakdown voltage of an insulator.

The breakdown voltage for diodes is the lowest reverse voltage that causes the diode to conduct noticeably in reverse. Some devices also have a forward breakdown voltage, such TRIACs(Triode for Alternating Current.).

2. What is Depletion Region?

The depletion region, also known as the depletion layer, depletion zone, in organic semiconductors, is an insulating region inside a conductive, doped semiconductor material where the mobile charge carriers have been diffused away or have been forced away by an electric field. Ionized donor or acceptor impurities are the sole elements present in the depletion area.

Rabert T

As an electrical engineer with 5 years of experience, I focus on transformer and circuit breaker reliability in 110/33-11kV and 33/11kV substations. I am a professional electrical engineer with experience in transformer service and maintenance. I understand electrical principles and have expertise troubleshooting, repairing, and maintaining transformers, circuit breakers, and testing them. Tweet me @Rabert_infohe

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