Zener breakdown and avalanche breakdown can occur in P-N junction diodes, depending on their specific characteristics, doping levels, and applied voltages.
Zener Breakdown
Zener breakdown occurs in heavily doped P-N junction diodes. In this mechanism, the electric field across the depletion region is intense enough to cause the valence electrons in the covalent bonds to break free, creating electron-hole pairs. These newly formed electron-hole pairs contribute to the flow of current, resulting in a sudden increase in current through the diode. Zener breakdown typically occurs when the reverse bias voltage exceeds the Zener voltage rating of the diode.
Avalanche Breakdown
Avalanche breakdown occurs in lightly doped P-N junction diodes. In this mechanism, the reverse bias voltage causes the minority charge carriers (either electrons in the p-region or holes in the n-region) to gain enough energy to collide with other atoms, dislodging additional charge carriers. This collision process creates an avalanche effect, rapidly increasing the number of charge carriers and leading to a significant increase in current. Avalanche breakdown typically occurs when the reverse bias voltage exceeds the avalanche voltage rating of the diode.