Avalanche breakdown

The avalanche breakdown, also called avalanche breakdown (of English avalanche, avalanche ), is one of the three types of breakdown in semiconductor devices. Under an opening of a pn junction is defined as the steep increase of the current at a given reverse voltage, when the diode is reverse biased. Trigger the avalanche breakdown is the avalanche effect (also avalanche effect, avalanche multiplication or multiplication called carrier ). The avalanche effect is a reversible or reversible effect, provided that the maximum power dissipation of the device is not exceeded.

Description

Charge carriers, which are moved by an external electric field by the space charge region, can knock out the valence electrons of the grid from their bonds and thus raise the conduction band by impact ionization. For sufficiently large external field strength, the electrons have such a great energy, that they not only make for a shock with the valence electrons of these as charge carriers available, but do not recombine themselves, remain in the conduction band and can generate free charge carriers again. This reduces the number of free charge carriers in the conduction band increases snowballed exponentially.

By the degree of doping the width of the space charge zone, and thus, the avalanche breakdown voltage can be changed in semiconductors. When avalanche breakdown, the current increases compared to the Zener breakdown, very abruptly with the voltage. As the temperature increases the avalanche breakdown begins only at higher voltage in contrast to the Zener breakdown. In general, act in practice Zener and avalanche effect simultaneously. The breakdown voltages are present here in the range between slightly under 6 and 8-10 V.

Functionally significant difference is that the avalanche breakdown has a positive temperature coefficient, as opposed to zener breakdown with negative temperature coefficient. The superposition and mutual compensation of both effects can thus produce relatively temperature stable zener diodes with threshold voltages ranging from 5.5V.

Application

The avalanche effect is used in the following semiconductor devices:

• Avalanche diodes operate with very high blocking voltage and use the avalanche effect, inter alia, for voltage stabilization and Schwingkreisentdämpfung ( IMPATT diode), as well as for the construction of noise generators.
• Avalanche photodiodes use of the avalanche effect to amplify the photocurrent
• Diodes and bipolar transistors can be protected by a controlled avalanche behavior from being destroyed by power surges. This method is used inter alia in the avalanche transistors which have a relatively high current and low transit times.
• Zener diodes with a breakdown voltage UZ > 5 V

• Solid State Physics