A strong electric field across a PN junction causes breakdown due to ______.

Avalanche breakdown occurs in a reverse-biased PN junction when the electric field becomes sufficiently strong to accelerate minority charge carriers to high energies. These carriers collide with semiconductor atoms and generate additional electron-hole pairs through impact ionization. The newly generated carriers are also accelerated, producing a chain reaction and a rapid increase in reverse current. Avalanche breakdown generally occurs at relatively higher reverse voltages and is associated with a wider depletion region than Zener breakdown.