Concept:In the breakdown region, the I-V curve is nearly vertical. This very low dynamic resistance (\( r_z = \Delta V_Z / \Delta I_Z \approx 0 \)) allows the diode to absorb large variations in reverse current with minimal change in terminal voltage.
Formula:$$\Delta V_Z = r_z \cdot \Delta I_Z \approx 0 \quad (\text{since } r_z \to 0)$$
Solution:- Because the reverse breakdown I-V characteristic is very steep, the dynamic resistance \( r_z \) is only a few ohms.
- Large changes in circuit current cause negligible changes in the voltage drop across the Zener diode, providing stable voltage regulation.
Why other options are incorrect:- Option B: A linear increase in barrier voltage would vary the output voltage, preventing stable voltage regulation.
- Option C: The depletion layer does not expand across the entire crystal; carrier tunneling maintains conduction within a thin junction.
- Option D: High carrier concentrations are actively generated via tunneling or impact ionization during breakdown.
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