Distinguish between zener breakdown and avalanche breakdown.

Explanation

`{:(,"Zener break down",,"Avalanche break down"),(1.,"Zener break down occurs at heavily doped diodes.",1.,"Avalanche break down occurs at lightly doped diodes."),(2.,"This occurs at low reverse bias voltages.",2.,"This occurs at high reverse bias voltages."),(3., "This occurs due to field emission.",3.,"This occurs due to ionisation by collision."),(4.,"Width of depletion layer is small.",4.,"Width of depletion layer is also small."):}`