Avalanche Breakdown and Zener Breakdown Effect Explained

In this video Avalanche breakdown and Zener breakdown effects in the PN junction diode have been explained.

Timestamps for various topics covered in this video are as follows:

0:18 Introduction,

1:50 Avalanche breakdown effect,

5:05 Zener diode and Zener breakdown effect,

9:00 Zener diodes Specifications,

10:36 Effect of temperature on Avalanche and Zener breakdown voltages.

The Avalanche breakdown effect:
In reverse bias condition, when the applied voltage across the PN junction diode, is more than the breakdown voltage (Vb) then suddenly a reverse saturation current shoots up.
Because at the applied breakdown voltage the electric field in the depletion region will be much stronger. And due to this electric field, the minority charge carriers will get accelerated. And due to enough kinetic energy, when they collide with the silicon atoms in the crystal, they can knock out the bound valance electrons of the atoms. Under the influence of electric field, the knocked out electrons (along with the previously accelerated electrons which have knocked out them) will again collide with the other silicon atoms and will knock out the bound valance electrons, In this way the number of free electrons increases in Geometric progression.

So, in this way, due to this impact ionization, a lot of minority charge carriers are generated in the depletion region. And due to that, the minority current will increase drastically. So, this effect is known as the avalanche breakdown effect and the voltage at which it occurs is known as the breakdown voltage. The Avalanche breakdown effect is seen in the lightly doped didoes.

Zener Breakdown effect:

The Zener effect is usually seen in the heavily doped diodes. (e.g Zener diodes)
In heavily doped diodes the depletion region is much narrower than the normal diodes. So, in reverse bias condition, at a specific voltage, the strength of the electric field in the depletion region is quite high, After a certain applied voltage, the electrons from the covalent bonds within the depletion region come out. And due to that, the electron-hole pair is created in the depletion region. Due to these additional minority carriers, there is a sudden rise in the reverse saturation current.
This effect is known as the Zener breakdown effect.
And the voltage at which this effect occurs is known as the Zener voltage.
The Zener effect occurs at a lower voltage than the avalanche effect. And in the Zener diodes, depending on the breakdown voltage, both effects are visible.
For the Zener diodes, whose breakdown voltage is in the range of 5.6V, the Zener effect is predominant.
While for the breakdown voltages, beyond 5.6V, the avalanche effect is predominant.
In a 5.6V Zener diode both effects occur together,

Effect of temperature on Zener and avalanche breakdown voltages:

As temperature increases, the Zener breakdown voltage reduces, So these diodes have Positive temperature coefficient (PTC)
While with temperature, the avalanche breakdown voltage increases, So these diodes have Negative temperature coefficient (NTC),
5.6V diodes both PTC and NTC cancels with each other, Thus 5.6V diodes are used in temperature critical applications.

This video will be helpful to all students of science and engineering in understanding the avalanche and Zener breakdown effect in PN junction diode.

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The link for the other useful videos:

1) PN Junction Diode
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2) Semiconductors (P-type and N-type)
   • Semiconductor: P-Type and N-Type, Int...  

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6) Half wave Rectifier
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7) Alternating current and Direct current
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