Concept:Under reverse bias, the mobile-carrier-free depletion layer behaves as a dielectric medium separating the conductive P and N regions, forming a voltage-variable capacitor (varactor).
Formula:$$C_j = \frac{\varepsilon A}{W} \quad (\text{where } W \propto \sqrt{V_{\text{reverse}}})$$
Solution:- The P and N bulk regions contain abundant mobile carriers and behave like parallel conducting plates.
- The depletion region between them is depleted of free carriers and acts as a dielectric insulator of width \( W \).
- This structure forms a junction transition capacitance \( C_j = \varepsilon A / W \).
Why other options are incorrect:- Option A: Inductive properties arise from magnetic flux linkage in coils, not electrostatic depletion layers.
- Option C: The charge storage across the depletion boundary introduces a reactive capacitive impedance.
- Option D: The junction stores charge electrostatically; it is not an active energy source.
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