Question

What does breakdown mean physically?

I saw this in wikipedia:

The avalanche process occurs when the carriers in the transition region are accelerated by the electric field to energies sufficient to free electron-hole pairs via collisions with bound electrons.

Say I have a lightly doped Germanium pn junction, will I be able to use it again or throw it away once Avalanche breakdown take place?

And also what happens in case of Zener breakdown? I know it requires highly doped pn junction and not so much pot diff..

Answer 1

The avalanche breakdown itself doesn't cause destruction, it just moves charge carriers around within the material.

But the breakdown results in extremely high currents through the semiconductor, which results in high temperatures. In particular with avalanche breakdown the higher the temperature gets, the higher the current becomes, which raises the temperature, etc. This results in a runaway thermal effect. The thermal stress is what causes physical destruction, e.g. melting.