Concept:A silicon diode requires a forward voltage greater than its built-in barrier potential (\( \approx 0.7\text{ V} \)) to reduce the depletion layer resistance and allow significant majority carrier conduction.
Formula:$$V_{\text{applied}} = 0.2\text{ V} < V_{\text{barrier}}(\text{Si}) \approx 0.7\text{ V}$$
Solution:- At \( V_{\text{applied}} = 0.2\text{ V} \), the external field only partially offsets the built-in potential barrier.
- The remaining potential barrier (\( \approx 0.5\text{ V} \)) continues to block the majority of diffusing charge carriers.
- Consequently, only a negligible sub-threshold current flows through the circuit.
Why other options are incorrect:- Option A: Breakdown occurs under high reverse voltage, not low forward voltage.
- Option B: The diode is forward-biased, but the voltage is below the threshold required for significant conduction.
- Option D: The semiconductor material remains functional; its operating point is simply below the forward knee voltage.
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