Avalanche breakdown
Encyclopedia
Avalanche breakdown 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
. The avalanche process occurs when the carriers in the transition region are accelerated by the electric field to energies sufficient to free electron-hole pairs via collisions with bound electrons.
may break free due to its thermal energy, creating an electron-hole pair. If there is a voltage gradient in the semiconductor, the electron will move towards the positive voltage while the hole will "move" towards the negative voltage. Most of the time, the electron and hole will just move to opposite ends of the crystal and stop. Under the right circumstances, however, (i.e. when the voltage is high enough) the free electron may move fast enough to knock other electrons free, creating more free-electron-hole pairs (i.e. more charge carriers), increasing the current. Fast-"moving" holes may also result in more electron-hole pairs being formed. In a fraction of a nanosecond, the whole crystal begins to conduct.
Avalanche breakdown usually destroys regular diodes, but avalanche diode
s are designed to break down this way at low voltages and can survive the reverse current.
The voltage at which the breakdown occurs is called the breakdown voltage. There is a hysteresis
effect; once avalanche breakdown has occurred, the material will continue to conduct if the voltage across it drops below the breakdown voltage. This is different from a Zener diode
, which will stop conducting once the reverse voltage drops below the breakdown voltage.
Electrical insulation
thumb|250px|[[Coaxial Cable]] with dielectric insulator supporting a central coreThis article refers to electrical insulation. For insulation of heat, see Thermal insulation...
and semiconducting
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
materials. It is a form of electric current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
multiplication that can allow very large currents within materials which are otherwise good insulators. It is a type of electron avalanche
Electron avalanche
An electron avalanche is a process in which a number of free electrons in a medium are subjected to strong acceleration by an electric field, ionizing the medium's atoms by collision , thereby forming "new" electrons to undergo the same process in successive cycles...
. The avalanche process occurs when the carriers in the transition region are accelerated by the electric field to energies sufficient to free electron-hole pairs via collisions with bound electrons.
Explanation
Materials conduct electricity if they contain mobile charge carriers. There are two types of charge carrier in a semiconductor: free electrons and electron holes. A fixed electron in a reverse-biased diodeDiode
In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...
may break free due to its thermal energy, creating an electron-hole pair. If there is a voltage gradient in the semiconductor, the electron will move towards the positive voltage while the hole will "move" towards the negative voltage. Most of the time, the electron and hole will just move to opposite ends of the crystal and stop. Under the right circumstances, however, (i.e. when the voltage is high enough) the free electron may move fast enough to knock other electrons free, creating more free-electron-hole pairs (i.e. more charge carriers), increasing the current. Fast-"moving" holes may also result in more electron-hole pairs being formed. In a fraction of a nanosecond, the whole crystal begins to conduct.
Avalanche breakdown usually destroys regular diodes, but avalanche diode
Avalanche diode
In electronics, an avalanche diode is a diode that is designed to go through avalanche breakdown at a specified reverse bias voltage. The junction of an avalanche diode is designed to prevent current concentration at hot spots, so that the diode is undamaged by the breakdown...
s are designed to break down this way at low voltages and can survive the reverse current.
The voltage at which the breakdown occurs is called the breakdown voltage. There is a hysteresis
Hysteresis
Hysteresis is the dependence of a system not just on its current environment but also on its past. This dependence arises because the system can be in more than one internal state. To predict its future evolution, either its internal state or its history must be known. If a given input alternately...
effect; once avalanche breakdown has occurred, the material will continue to conduct if the voltage across it drops below the breakdown voltage. This is different from a Zener diode
Zener diode
A Zener diode is a special kind of diode which allows current to flow in the forward direction in the same manner as an ideal diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, "Zener knee voltage" or "Zener...
, which will stop conducting once the reverse voltage drops below the breakdown voltage.