What is Avalanche Breakdown

Minority carriers, under reverse biased conditions, flowing through  the  junction  acquires  a  kinetic  energy  that increases  with  increase  in reverse  voltage.   At  a  sufficiently  high  reverse  voltage  (say  5v  or  more),  kinetic energy  of  minority  carriers  becomes  so  large  that  they  knock  out  electrons  from  the covalent  bonds  of  semiconductor  material.   As  a result  of  collision,  liberated electrons in turn liberate more electrons and current becomes very large leading the breakdown  of  crystal  structure  itself.    This  phenomenon  is  known as Avalanche Breakdown.