Avalanche breakdown (or the avalanche effect) is a phenomenon that can occur in both insulating and semiconducting materials. It is a form of electric current multiplication that can allow very large currents within materials which are otherwise good insulators. It is a type of

electron avalanche An electron avalanche is a process in which a number of free electrons in a transmission medium are subjected to strong acceleration by an electric field and subsequently collide with other atoms of the medium, thereby ionizing them ( impact ioniz ...

. The avalanche process occurs when carriers in the transition region are accelerated by the electric field to energies sufficient to create mobile or free

electron The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...

hole A hole is an opening in or through a particular medium, usually a solid Body (physics), body. Holes occur through natural and artificial processes, and may be useful for various purposes, or may represent a problem needing to be addressed in m ...

pairs via collisions with bound electrons.

Explanation

Materials conduct electricity if they contain mobile charge carriers. There are two types of charge carriers in a semiconductor: free electrons (mobile electrons) and electron holes (mobile holes which are missing electrons from the normally-occupied electron states). A normally-bound electron (e.g., in a bond) in a reverse-biased

diode A diode is a two-Terminal (electronics), terminal electronic component that conducts electric current primarily in One-way traffic, one direction (asymmetric electrical conductance, conductance). It has low (ideally zero) Electrical resistance ...

may break loose due to a thermal fluctuation or excitation, creating a mobile electron-hole pair (

exciton An exciton is a bound state of an electron and an electron hole which are attracted to each other by the electrostatic Coulomb's law, Coulomb force resulting from their opposite charges. It is an electrically neutral quasiparticle regarded as ...

). If there is a voltage gradient (electric field) in the semiconductor, then the electron will move towards the positive voltage while the hole will move towards the negative voltage. Usually, the electron and hole will simply move to opposite ends of the crystal and enter the appropriate electrodes. When the electric field is strong enough, the mobile electron or hole may be accelerated to speeds high enough to knock other bound electrons free, creating more free charge carriers, increasing the current and leading to further "knocking out" processes and creating an avalanche. In this way, large portions of a normally-insulating crystal can begin to conduct. The large voltage drop and possibly large current during breakdown necessarily leads to the generation of heat. Therefore, a diode placed into a reverse blocking power application will usually be destroyed by breakdown if the external circuit allows a large current. In principle, avalanche breakdown only involves the passage of electrons and need not cause damage to the crystal. Avalanche diodes (commonly encountered as high voltage

Zener diode A Zener diode is a type of diode designed to exploit the Zener effect to affect electric current to flow against the normal direction from anode to cathode, when the voltage across its terminals exceeds a certain characteristic threshold, the ''Z ...

s) are constructed to break down at a uniform voltage and to avoid current crowding during breakdown. These diodes can indefinitely sustain a moderate level of current during breakdown. The voltage at which the breakdown occurs is called the

breakdown voltage The breakdown voltage of an insulator (electrical), insulator is the minimum voltage that causes a portion of an insulator to experience electrical breakdown and become electrically Conductor (material), conductive. For diodes, the breakdown vo ...

. There is a

hysteresis Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of ...

effect; once avalanche breakdown has occurred, the material will continue to conduct even if the voltage across it drops below the breakdown voltage. This is different from a

, which will stop conducting once the reverse voltage drops below the breakdown voltage.

References

*Microelectronic Circuit Design — Richard C Jaeger — *The Art of Electronics — Horowitz & Hill —
University of Colorado guide to Advance MOSFET design
*
Power MOSFET avalanche characteristics and ratings
- ST Application Note AN2344
Power MOSFET Avalanche Design Guidelines
- Vishay Application Note AN-1005 {{DEFAULTSORT:Avalanche Breakdown Electrical breakdown

Explanation

See also

References