Concept:Transition capacitance (\( C_T \)) arises from changes in the space-charge layer with reverse voltage, while diffusion capacitance (\( C_D \)) arises from the storage of injected minority carriers near the junction edges during forward conduction.
Formula:$$C_T = \frac{\epsilon_s A}{W} \propto (V_0 + V_R)^{-1/2} \quad (\text{Dominates in Reverse Bias})$$
$$C_D = \frac{\tau I_F}{\eta V_T} \propto I_F \quad (\text{Dominates in Forward Bias})$$
Solution:- In reverse bias, the depletion layer acts as a voltage-variable capacitor dielectric, making \( C_T \) the dominant capacitance.
- In forward bias, injected minority carriers accumulate outside the depletion region, creating a large diffusion capacitance \( C_D \) proportional to forward current \( I_F \).
Why other options are incorrect:- Option A: This reverses the operating bias domains for \( C_T \) and \( C_D \).
- Option B: Both capacitances depend strongly on applied voltage and current.
- Option D: Junction capacitance is an internal solid-state semiconductor property.
Quality & Fidelity Assurance:
Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.