Understanding Avalanche Diodes: A Guide For Engineers

As an engineer, you know how important diodes are to the way electronic circuits work.

But do you know about the avalanche diode? Avalanche diodes are different from regular diodes because they have a special feature that lets them do a number of different tasks in high voltage applications.

So buckle up and get ready to dive into the fascinating world of avalanche diodes!

Introduction to Avalanche Diode

Formal definition:

A semiconductor breakdown diode, usually made of silicon, in which avalanche breakdown occurs across the entire pn junction and voltage drop is then essentially constant and independent of current; the two most important types are IMPATT and TRAPATT diodes.

An avalanche diode is a type of semiconductor diode that is made to break down in an avalanche at a certain voltage.

When the voltage across a diode goes above a certain value, avalanche breakdown happens.


A Zener diode and an avalanche diode are both made the same way, but the amount of doping in an avalanche diode is different from that in a Zener diode.

The junction of an avalanche diode is made to stop current concentration and the hot spots that come from it, so that the avalanche effect does not hurt the diode.

Working Principle of Avalanche Diode

Avalanche diodes are made to work in the reverse breakdown region, where they can carry a large current without being damaged.

The pn junction of an avalanche diode is made to stop current concentration and the hot spots that come from it, so that the avalanche effect does not hurt the diode.

When a reverse bias voltage is applied to the avalanche diode, it reaches the breakdown voltage and goes into the avalanche breakdown region, where it can carry a large current without being damaged.

Avalanche breakdown happens when the voltage across the diode is higher than a certain value, which makes the current rise quickly.

Avalanche multiplication makes more free electrons and ions, which causes a large amount of current to flow through the device.

Types of Avalanche Diodes

Zener Diode

The Zener diode is a type of diode that shows the Zener breakdown effect when the voltage across the diode goes above a certain level.

A high electric field across the diode causes the Zener breakdown effect, which is a type of avalanche breakdown.

The Zener diode is mostly used to control the voltage, protect against surges, and make noise.

Avalanche Photodiode

The avalanche photodiode is a type of semiconductor diode that is made to work in the avalanche breakdown region.

It is often used as a high-gain photon detector in low-light applications like fiber optic communication systems and imaging devices.

When photons are taken in by the diode, they create electron-hole pairs

The high electric field in the diode can then speed up these electron-hole pairs, causing a flood of charge carriers.

Difference between Zener and Avalanche Breakdown

The way that Zener breakdown and avalanche breakdown happen is the main difference between the two.

Zener breakdown happens when there is a strong electric field across the diode's depletion region

Avalanche breakdown happens when free electrons hit atoms in the diode.

The amount of doping in a diode determines the Zener breakdown voltage, while the width of the depletion region determines the avalanche breakdown voltage.

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Applications of Avalanche Diodes

Protection Devices and Voltage Regulators

Most of the time, avalanche diodes are used to protect sensitive electronic parts from being damaged by high voltage or current surges in electronic circuits.

They can also be used to control the voltage across a load in circuits, where they work in the reverse breakdown region.

Noise Sources in RF and Microwave Circuits

In RF and microwave circuits, avalanche diodes are often used as noise sources.

During the avalanche breakdown process, electrons and holes are made at random, which makes white noise

This makes them useful for communication and electronic warfare.

High-Speed Switching Devices in Digital Circuits

In digital circuits, avalanche diodes are used as high-speed switches that can turn on and off in a very short amount of time, called a picosecond.

Because of this, they can be used for things like high-speed data transfer and digital signal processing.

High-Gain Photon Detectors in Optoelectronic Systems

Avalanche photodiodes (APDs) are semiconductor devices that are made to work in the avalanche breakdown region when photons are absorbed by the diode.

APDs are used in fiber-optic communication systems, laser ranging systems, and other low-light-level applications as high-gain photon detectors.

Voltage Drop in Avalanche Diodes

Avalanche diodes are designed to take advantage of the avalanche effect, so they have a small but noticeable voltage drop when they break down.

Zener diodes, on the other hand, always keep the voltage above the point where they break down.

Most avalanche diodes have a voltage drop of between 1 and 2 volts.

Temperature Coefficient of Voltage

Zener diodes have a small temperature coefficient of voltage that is negative, while Avalanche diodes have a small temperature coefficient of voltage that is positive.

This means that as the temperature goes up, the voltage drop in an avalanche diode will go up slightly, while the voltage drop in a Zener diode will go down as the temperature goes up.

Comparison with Other Diodes

Most Schottky diodes have a voltage drop of between 0.15V and 0.45V.

The forward voltage for Silicon Diodes is 0.7V, and for Germanium Diodes it is 0.3V.

As the forward voltage drop across a silicon diode is almost constant at about 0.7v, while the current through it varies by relatively large amounts, a forward-biased silicon diode can be used as a constant-voltage source.

Advantages and Disadvantages of Using Avalanche Diodes

Avalanche diodes have several advantages over normal diodes. They last longer than most diodes, which makes them more reliable when used in certain situations.

The pn junction of an avalanche diode is designed to prevent current concentration and resulting hot spots so that the diode is undamaged by the avalanche effect.

The advantages

Avalanche diodes are useful in a number of situations, such as protecting circuits, making noise, and finding photons.

They exhibit a greater level of sensitivity, high performance, and fast response time, making them ideal for use in these applications.

They can also protect circuits from voltages that should not be there, which makes them useful in electronic systems.

The disadvantages

But there are some bad things about using avalanche diodes that you should think about.

These include the need for a much higher operating voltage, a non-linear output caused by the avalanche process, a much higher level of noise, and the need for a high reverse bias to work.

Avalanche diodes may also not work as well as other types of diodes, which could be a problem in some situations.

Even though they have these problems, avalanche diodes are still widely used in certain situations because of how they work.

Even though they may not be as reliable as other types of diodes, they are useful in electronic systems because they are sensitive and respond quickly.

Difference Between Avalanche Diode and PIN Diode

Avalanche diodes and PIN diodes are both types of semiconductor diodes, but they work in very different ways.

Operating Voltage

The running voltage is a big difference between the two types.

Avalanche diodes are made to work in the reverse breakdown region, which needs a higher voltage than the normal operating region.

PIN diodes, on the other hand, work in the forward-biased region, which usually needs less voltage.

So, it is better to say that avalanche diodes need a higher voltage to reach the avalanche breakdown region than that they need a higher operating voltage.


Because of how they work, avalanche diodes can make more noise.

But this noise level can be lowered by applying a voltage in the opposite direction of the breakdown voltage.

PIN diodes, on the other hand, are usually used because they make less noise, but they can still make some noise depending on how they are being used.

Internal Structure

Avalanche diodes have a place inside where electrons multiply when a reverse voltage is applied from the outside.

This makes the internal amplification between 10 and 100 times bigger.

On the other hand, PIN diodes have an intrinsic region that has a larger depletion region and less capacitance than a standard p-n diode.

This means that PIN diodes are more sensitive and respond more quickly.

Voltage Requirements

Avalanche diodes have a reverse bias voltage that is much higher, between 100 and 200 volts for silicon.

The PIN diode, on the other hand, works at a low voltage and is good for low-power devices.

Overall, avalanche diodes and PIN diodes are made in similar ways, but their different ways of working mean that they are used in different situations.

Avalanche diodes can be used with high voltages, and in optoelectronic systems, they can be used as high-gain photon detectors.

On the other hand, PIN diodes are better for low-power, high-frequency applications that need both low noise and high speed.

Low Noise Avalanche Diodes

Avalanche photodiodes are the correct name for low-noise avalanche diodes (APDs).

APDs are semiconductor photodiode detectors that use the photoelectric effect to turn light into electricity. They are very sensitive.

Their high signal-to-noise ratio (SNR), fast time response, low dark current, and high sensitivity are what make them stand out.

Applications of APDs

APDs are used for many different things, such as:

  • Laser range finders.
  • Studies of photon correlation.
  • Systems for communicating with fiber optics.
  • Lidar.
  • Scanners for PET, or positron emission tomography.

Low-Noise Bias Circuit

The gain of an APD is controlled by the voltage that is put across the junction in the opposite direction. To keep the gain steady and the noise level low, this voltage needs to be carefully controlled.

To do this, the bias voltage for APDs can be made and controlled by a low-noise bias circuit. This circuit uses a PWM boost converter with a fixed frequency and low noise

A microcontroller that reads a thermistor compensates for temperature.

Excess Noise Factor

Compared to PIN photodiodes, APDs have more noise because the statistics of the avalanche process cause current fluctuations.

The excess noise factor is a way to calculate how much more noise an APD has than a shot noise limited detector.

Avalanche Photodiodes

A highly sensitive semiconductor photodiode detector, an avalanche photodiode (APD) uses the photoelectric effect to turn light into electricity.

The APD works with a high reverse bias, which lets the holes and electrons made when a photon or light hits it multiply like avalanches.

This makes it possible to boost the gain of the photodiode several times, giving it a wide range of sensitivity.

How avalanche multiplication process works in APDs

The avalanche process starts when a photon is absorbed and an electron or a hole is ionized when they hit something.

The electric field gives the resulting carriers enough energy to make secondary carriers through impact ionization.

This process makes a flood of electron-hole pairs, which gives a stronger signal than direct absorption alone.

The gain of the APD is equal to the ratio of the total number of electrons and holes made by the avalanche process to the number of photons absorbed by the device.

Advantages and Disadvantages

The main benefit of an avalanche photodiode is that it is very sensitive and can pick up low-level signals.

The APD is more sensitive than other semiconductor photodiodes and can be used in places where other photodiodes may not be able to reach the same level of sensitivity.

Compared to other types of photodiodes, the APD also responds faster and has less current flow when it is not being used.

APDs do have some problems, though.

  • One of the main problems with an APD is that, compared to other photodiodes, it needs a higher voltage to work.
  • Due to carrier multiplication, APDs also make more noise than they should.
  • Using the right design techniques and operating conditions can cut down on the noise.
  • Lastly, an APD does not have a linear output, which can make it harder to use in some situations.

Use cases

Used in:Description:
Voltage RegulatorsAvalanche diodes can be used to control the voltage in electronic circuits by providing a stable reference voltage. They can be used as a shunt regulator to keep the voltage constant across the circuit or as a series regulator to keep the output voltage stable even if the voltage coming in changes.
Pulse GeneratorsAvalanche diodes can be used to make short bursts of high voltage in pulse generators. When a voltage spike happens, the diode goes into avalanche breakdown and makes a sharp pulse with a fast rise time. This is useful for things like radar, which need pulses with a high frequency.
Microwave DevicesIMPATT (IMPact ionization Avalanche Transit-Time) and TRAPATT (TRApped Plasma Avalanche Triggered Transit) diodes use avalanche diodes. These diodes send out high-frequency signals in the microwave range These signals are used in radar systems, satellite communication systems, and other high-frequency applications.
Surge ProtectionAvalanche diodes can be used in surge protectors to protect electronic devices from voltage spikes and transient overvoltages. They can clamp the voltage at a certain level and keep the device from being damaged by high voltage.
RF AmplifiersRadio frequency (RF) amplifiers can use avalanche diodes to make high-power RF signals. In this case, the diode goes into the avalanche breakdown region, which causes the current to rise quickly and make a strong RF signal.
X-ray and Gamma Ray DetectorsAvalanche diodes can be used in medical imaging and other places as X-ray and gamma ray detectors. Photons with a lot of energy are picked up by the diode, which sends out a pulse of current that can be used to measure the energy of the radiation.

Other uses:



As this article comes to a close, it is clear that avalanche diodes are important parts of many electronic systems.

Because of how they are made and what they can do, they are useful tools for any engineer.

But, like any other technology, using avalanche diodes has both pros and cons, and it is important to weigh these carefully in any application.

As engineers, we are always looking for the newest and best technology to help us design better systems.

But it is also important to keep in mind that the basics of electronics have been around for a long time and are just as important today as they were then.

So, whether you are an experienced engineer or just getting started, it is important to know how avalanche diodes work in modern electronics.

By doing this, you will be better able to design systems that work well and are reliable for your applications.

Even though technology changes, the basic rules of electronics stay the same.

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