Question

Draw diagram for a P-N junction to obtain reverse bias characteristic curves. Explain the phenomenon of reverse breakdown for a P-N junction in reserve bias state by following processes-
(i) Avalanche breakdown
(ii) Zener breakdown

Answer 1

When we connect PN junction diode in reverse condition the minority from both side of PN diode move hence the reverse current flow.
When we increase the reverse voltage the depletion layer breaks at certain reverse voltage this voltage is known as break down voltage.
The break down of depletion layer can be two type.
(1) Avalanche breakdown : the minority charge carrier get highly accelerated. The kinetic energy becomes high enough at they knock-off electrons from the covalent bonds of semiconductors. The newly generated electron holes pairs also accelerated and cause ionisation the depletion layer & break down the depletion layer.
(2) Zener breakdown : Due to high doping in zener diode the depletion layer has small width. When large reverse biased applied across such a diode, the depletion layer & the energy bands get modified, As the depletion width is very small, small voltage will set high electric field of $4\times {10}^{7}V/m$. this high electric field strips off many electrons from valence band which tunnel to the n-side through the this depletion layer. It gives rise to a large reverse current or breakdown current this breakdown in a diode due to the band to band tunneling is called zener breakdown.