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Chapter: Electronic Devices - Special Semiconductor Devices

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Difference between Zener breakdown from avalanche breakdown

Zener Breakdown: 1.This occurs at junctions which being heavily doped have narrow depletion layers . Avalanche breakdown: 1.This occurs at junctions which being lightly doped have wide depletion layers.

Difference between Zener breakdown from avalanche breakdown


 

Zener Breakdown

1.This occurs at junctions which being heavily doped have narrow depletion layers .

2.This breakdown voltage sets a very strong electric field across this narrow layer.

3.Here electric field is very strong to rupture the covalent bonds thereby generating electron-hole pairs. So even a small increase in reverse voltage is capable of producing large number of current carriers. i.e. why the junction has a very low resistance. This leads to Zener breakdown.

 

Avalanche breakdown

1.This occurs at junctions which being lightly doped have wide depletion layers.

2.Here electric field is not strong enough to produce Zener breakdown.

3.Her minority carriers collide with semi conductor atoms in the depletion region, which breaks the covalent bonds and electron-hole pairs are generated. Newly generated charge carriers are accelerated by the electric field which results in more collision and generates avalanche of charge Carriers. This results in avalanche breakdown.

 


Zener diode characteristics

 

The Zener Diode is used in its "reverse bias" or reverse breakdo wn mode, i.e. the diodes anode connects to the negativ e supply. From the I-V characteristics curv e above, we can see that the zener diode has a regio n in its reverse bias characteristics of almost a constant negative voltage regardless of the value of the current flowing through the di ode and remains nearly constant even with large cha nges in current as long as the zener diodes current remains between the breakdown current IZ(min) and the maximum current rating IZ(max).


Figure 4.7 Zener diode characteristics 

 


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