What is Avalanche Breakdown in a P-N Junction Diode?

• When a diode is heavily reverse-biased, the depletion region widens, and a very strong electric field is created.
• The few minority charge carriers (electrons and holes) present in the depletion region are accelerated to incredibly high speeds by this electric field.
• These fast-moving carriers collide violently with the atoms in the crystal lattice, knocking out bound electrons and creating new electron-hole pairs.
• These newly freed carriers are also accelerated and collide with more atoms, freeing even more carriers. This chain reaction multiplies the charge carriers exponentially—much like a snow avalanche on a mountain.

This sudden, explosive multiplication of charge carriers causes a massive surge of reverse current. If the circuit does not have a current-limiting resistor, the enormous heat generated by this current will completely destroy the diode.

While both cause a surge in reverse current:

• Zener Breakdown occurs in heavily doped diodes at lower voltages (usually below 6V). The electric field simply tears electrons directly out of their bonds.
• Avalanche Breakdown occurs in lightly doped diodes at higher voltages (usually above 6V) due to the physical collision of fast-moving carriers.