Question

what is internal field emission?

Answer 1

Internal field emission is also called zener break down. Zener breakdown occurs in heavily doped pn junctions, i.e. in a zener diode. The depletion layer of a highly doped pn junction is extremely thin. At high voltage electrons jump from valance band to conduction band. But the current can still be controlled by changing the voltage. So, zener breakdown doesn’t damage the diode.