Concept:During forward conduction, excess minority carriers are stored near the depletion layer edges. When reverse bias is suddenly applied, these stored charges produce a transient reverse current pulse until they are removed via drift and recombination over the reverse recovery time \( t_{rr} \).
Formula:$$t_{rr} = t_s \text{ (storage time)} + t_t \text{ (transition time)}$$
Solution:- In forward bias, large numbers of minority carriers are injected across the junction and stored in the neutral regions.
- When the applied voltage switches to reverse bias, these stored carriers flow backward as a substantial reverse current.
- The diode recovers its blocking state only after these carriers are swept out or recombine, over the duration \( t_{rr} \).
Why other options are incorrect:- Option A: Packaging lead inductance is negligible compared to carrier storage effects at standard switching speeds.
- Option B: Air dielectric breakdown does not occur at normal operating voltages.
- Option D: Dopant atoms are chemically stable and do not undergo nuclear decay.
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