Help with the Key Points of Zener Breakdown and Avalanche Breakdown

In summary, the conversation discusses the differences between Zener and Avalanche breakdown in diodes. Zener breakdown occurs when the field strength exceeds a critical value, causing an explosive rise in current. On the other hand, Avalanche breakdown occurs at high velocities of minority carriers, leading to a similar explosive rise in current. The temperature dependencies of both effects have different signs, with Zener having a negative tempco and Avalanche having a positive tempco. At a Z-voltage of 5.6 volts, the temperature effects almost cancel out. The conversation also raises questions about the role of doping and the constant current in these breakdown processes.
  • #1
Stonestreecty
20
3
TL;DR Summary
The avalanche breakdown occurs because of the ionisation of electrons and hole pairs whereas the Zener breakdown occurs because of heavy doping. The Zener and the avalanche effect may occur simultaneously or independently of one another in PN junction. What the key points of them?
Good day, all
I am familiar with both of terms that I speak of in title. But I cannot find a full answer, so I might as well ask the PhD'ers here. What is really happening in Zener and Avalanche breakdown? I have read Guide to Zener Effect and Avalanche Effect and still feel confused.
And yes I get that impact ionization thing etc. But still, how does Zener differ from Avalanche breakdown? Why is doping so important? How come it doesn't damage the diode? Why is current constant? Why would it be constant when u exceeded the depletion zone(reverse bias), current should be proportional to voltage? (more voltage, more energy, more charges pulled out, more current) I am trying to get a full picture here. You may post something with detailed quantum mechanics, semiconductor theory.

Thank you in advance. :smile:
 
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  • #2
1.) Z (Zener) diode:
When the field strength exceeds the critical value of about 1E5 V/cm, the field forces are so strong that the electrons are torn out of the lattice. This causes the current to rise explosively.

2.) Avalanche diode:
At very high velocities of the minorities, there is a secondary effect where more charged carriers are torn out of the lattice - and the current rises explosively (like an avalanche)

3.) It is important that the temperature dependencies of both effects have different signs: The tempco is negative for Zener effects (Vz<5.6 volts) and positive for avalanche effects (Vz>5.6 volts).
At a Z-voltage of about Vz=5.6 volts, both temperature effects almost compensate each other.
 
  • Informative
Likes berkeman

What is Zener breakdown?

Zener breakdown is a phenomenon that occurs in a reverse-biased diode when the electric field is strong enough to cause a significant number of covalent bonds to break and create free electrons and holes. This results in a sudden increase in current through the diode, allowing it to conduct in the reverse direction.

What is avalanche breakdown?

Avalanche breakdown is a similar phenomenon to Zener breakdown, but it occurs at much higher voltages. In this case, the electric field is strong enough to accelerate free electrons and create more electron-hole pairs through collisions with atoms in the semiconductor material. This results in a rapid increase in current and can potentially damage the diode.

What are the key points to remember about Zener breakdown?

The key points to remember about Zener breakdown are:

  • It occurs in reverse-biased diodes.
  • It occurs at lower voltages than avalanche breakdown.
  • It is caused by the breakdown of covalent bonds in the diode material.
  • It results in a sudden increase in current through the diode.
  • It is a reversible phenomenon and the diode will return to its normal state once the voltage is reduced.

What are the key points to remember about avalanche breakdown?

The key points to remember about avalanche breakdown are:

  • It also occurs in reverse-biased diodes.
  • It occurs at higher voltages than Zener breakdown.
  • It is caused by the creation of more electron-hole pairs through collisions.
  • It results in a rapid increase in current and can potentially damage the diode.
  • It is an irreversible phenomenon and the diode may be permanently damaged.

How can Zener and avalanche breakdown be prevented?

Zener and avalanche breakdown can be prevented by using a series resistor to limit the current through the diode, or by using a voltage regulator circuit that maintains a constant voltage across the diode. Additionally, selecting a diode with a higher breakdown voltage can also prevent these breakdowns from occurring.

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