In electronics, an avalanche diode is a diode (made from

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...

or other

semiconductor A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...

) that is designed to experience avalanche breakdown at a specified reverse bias

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge t ...

. The junction of an avalanche diode is designed to prevent current concentration and resulting hot spots, so that the diode is undamaged by the breakdown. The avalanche breakdown is due to minority carriers accelerated enough to create ionization in the crystal lattice, producing more carriers, which in turn create more ionization. Because the avalanche breakdown is uniform across the whole junction, the breakdown voltage is nearly constant with changing current when compared to a non-avalanche diode. The

Zener diode A Zener diode is a special type of diode designed to reliably allow current to flow "backwards" (inverted polarity) when a certain set reverse voltage, known as the ''Zener voltage'', is reached. Zener diodes are manufactured with a great var ...

exhibits an apparently similar effect in addition to Zener breakdown. Both effects are present in any such diode, but one usually dominates the other. Avalanche diodes are optimized for avalanche effect, so they exhibit small but significant voltage drop under breakdown conditions, unlike Zener diodes that always maintain a voltage higher than breakdown. This feature provides better surge protection than a simple Zener diode and acts more like a gas-discharge tube replacement. Avalanche diodes have a small positive temperature coefficient of voltage, whereas diodes relying on the Zener effect have a negative temperature coefficient.

Uses

Voltage reference

The voltage after breakdown varies only slightly with changing current. This makes the avalanche diode useful as a type of voltage reference. Voltage reference diodes rated more than about 6–8 volts are generally avalanche diodes.

Protection

A common application is to protect

electronic circuit An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow. It is a type of electri ...

s against damaging high voltages. The avalanche diode is connected to the circuit so that it is reverse-biased. In other words, its

cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction i ...

is positive with respect to its

anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemoni ...

. In this configuration, the diode is non-conducting and does not interfere with the circuit. If the voltage increases beyond the design limit, the diode goes into avalanche breakdown, causing the harmful voltage to be conducted to ground. When used in this fashion, they are often referred to as clamping diodes or transient-voltage suppressors because they fix or "clamp" the maximum voltage to a predetermined level. Avalanche diodes are normally specified for this role by their clamping voltage ''V''_BR and the maximum amount of transient energy they can absorb, specified by either energy (in

joule The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applie ...

s) or

i^2rt

. Avalanche breakdown is not destructive as long as the diode is prevented from overheating.

Radio-frequency noise generation

Avalanche diodes generate radio-frequency noise. They are commonly used as noise sources in radio equipment and hardware random number generators. For instance, they are often used as a source of RF for antenna analyzer bridges. Avalanche diodes can also be used as

white noise In signal processing, white noise is a random signal having equal intensity at different frequencies, giving it a constant power spectral density. The term is used, with this or similar meanings, in many scientific and technical disciplines, ...

generators.

Microwave-frequency generation

If placed into a resonant circuit, avalanche diodes can act as negative-resistance devices. The IMPATT diode is an avalanche diode optimized for frequency generation.

Single-photon avalanche detector

These are made from doped silicon and depend on the avalanche breakdown effect to detect even single photons. The silicon avalanche photodiode is a high-gain photon detector. They are "ideal for use in high-speed, low-light-level applications".Advanced Photonix. The avalanche photodiode is operated with a reverse bias voltage of up to hundreds of volts, slightly below its breakdown voltage. In this regime, electron–hole pairs generated by the incident photons take a large amount of energy from the electric field, which creates more secondary charge carriers. The photocurrent of just one photon can be registered with these electronic devices.

References

{{DEFAULTSORT:Avalanche Diode Diodes Voltage stability