PN-junction Breakdown: Sudden Increase in Reverse Current

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SUMMARY

The sudden increase in reverse saturation current at the breakdown voltage in a PN-junction diode is primarily due to the phenomenon of breakdown, which occurs when the applied voltage exceeds the junction's capacity. This breakdown can be likened to an arc through the junction, leading to localized crystal melting and creating a low resistance "short" in parallel with the junction. While breakdown can result in irreversible damage, it is the rapid generation of carriers through mechanisms such as impact ionization and tunneling across the bandgap that triggers this increase in current flow.

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Why there is sudden increase in the small reverse saturation current at the breakdown voltage in PN-junction Diode?
 
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The phenomenon is called "breakdown" because the junction is literally broken. A typical failure mechanism when the applied voltage gets too big is equivalent to an arc through the junction, resulting in localized crystal melting. This in turn puts a low resistance "short" in parallel with the junction, giving rise to large current flow.
 
marcusl said:
The phenomenon is called "breakdown" because the junction is literally broken. A typical failure mechanism when the applied voltage gets too big is equivalent to an arc through the junction, resulting in localized crystal melting. This in turn puts a low resistance "short" in parallel with the junction, giving rise to large current flow.

Although breakdown can cause irreversible damage to a junction, that's not the cause but a possible effect of the high current.

Generally, breakdown occurs when a large number of carriers are generated very quickly, via impact ionization for example, or when carriers can tunnel across the junction through the bandgap.
 

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