Concept:Heavy doping produces an extremely narrow depletion region (\( < 10^{-6}\text{ m} \)), generating an intense electric field (\( > 10^6\text{ V/m} \)) at low reverse voltages that pulls electrons directly out of covalent bonds.
Formula:$$E = \frac{V}{d} \quad (\text{where } d \text{ is very small, so } E \text{ is extremely large})$$
Solution:- In heavily doped diodes (typically with breakdown voltage \( V_Z < 6\text{ V} \)), high internal fields cause quantum tunneling/direct field ionization of covalent bonds.
- This mechanism is known as Zener breakdown.
Why other options are incorrect:- Option B: Thermal runaway is destructive heating caused by excessive power dissipation.
- Option C: Avalanche breakdown occurs in lightly doped junctions via collision/impact ionization at higher voltages (\( > 6\text{ V} \)).
- Option D: Dielectric polarization is the displacement of bound charges in an insulator under an external field.
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