When a p-n junction is forward biased then its energy-band diagram looks like this:

enter image description here

What would happen if $V_a>V_{bi}$? ($V_{bi}$ is the built-in potential and $V_a$ is the externally applied voltage). Apparently, the bands would "reverse", in the sense that the conduction band limit in the p-side will be lower that the conduction band limite in the n-side; the same would happen with the valence band.

What's the meaning of this? Can this happen?


No the energy band would not reverse. As we increase the applied volatge the drop across the nuentral region increases such that the n side depletion region is always higher in potential to the p side depletion region.

Actually :

Depletion potential = (built in potential) -{(applied potential)-(potential drop across neutral region) }

But at lower applied bias the potential drop across the netrual region is negligible and gains prominence at higher applied bias.


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