# Why doesn't electron from p junction jump into the conduction band of n junction during reverse bias?

When reverse bias is applied, why can't electrons from p region that are currently occupying the holes jump into the conduction band of the n region, which according to the image (taken from hyperphysics) would not require extra energy, thus completing the circuit?

But this doesn't seem to happen since the current is negligible during reverse bias,why?

When reverse bias is applied, why can't electrons from p region that are currently occupying the holes jump into the conduction band of the n region, which according to the image (taken from hyperphysics) would not require extra energy, thus completing the circuit?

They can and do. This is called "band to band tunneling". However the probability of band to band tunneling is a strong function of the barrier width. It only typically becomes significant when that barrier is a few nm or narrower. Most diodes are designed to avoid it. Zener diodes are designed to make use of this behavior.

• Can you explain why electron transfer from conduction band of n to valence band of p is then possible even with a field (in the depletion region) pushing the electrons in the opposite way, I want to understand why one of the process happens and the other doesn't.
– veke
Commented Aug 8, 2023 at 13:23
• Also why can't the depletion region itself decrease, since electrons in the depletion region in the p side can jump to the conduction band of n?
– veke
Commented Aug 8, 2023 at 13:57
• @veke Electrons can tunnel either way depending on the applied bias. (Band to band tunneling in forward bias gives you an Esaki diode or backward diode depending on band alignment.) Depending on the density of filled and vacant states the probabilities will vary. Im not sure I fully understand what you are asking here though.
– Matt
Commented Aug 8, 2023 at 21:43
• Thank you for your answers, I wanted to know why current doesn't flow in reverse bias but does so in forward bias, if it is due to to the width of the depletion region ,I want to know why the negative charges in p type depletion region don't jump to the conduction band of n type thus minimizing the depletion width and thus conducting current during reverse bias.
– veke
Commented Aug 9, 2023 at 4:30
• @veke Thats really a different question than the one here. But... The negative charges in the p side of the depletion region are ionized acceptors. They are fixed charges, part of the semiconductor crystal lattice, and they cannot move.
– Matt
Commented Aug 9, 2023 at 11:07