Concept:Under forward bias, injected minority carriers accumulate near the edges of the depletion region before recombining. The rate of change of this stored charge with forward voltage defines the diffusion capacitance \( C_D \).
Formula:$$C_D = \frac{d Q}{d V_F} = \tau \left(\frac{d I_F}{d V_F}\right) = \frac{\tau I_F}{\eta V_T} \propto I_F$$
Solution:- In forward bias, large numbers of minority carriers are injected across the junction.
- The resulting stored charge increases with forward current, making diffusion capacitance \( C_D \) much larger than transition capacitance \( C_T \).
Why other options are incorrect:- Option A: Transition capacitance \( C_T \) is dominant in reverse bias, where the depletion layer acts as a dielectric between two conductive regions.
- Option B: Diodes do not use air-gap dielectrics.
- Option C: Stray inductance is an unwanted parasitic property of packaging leads, not an internal junction property.
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