Concept:Above the knee voltage, the internal potential barrier is fully overcome. The dynamic resistance is then determined primarily by the small resistance of the neutral bulk semiconductor regions.
Formula:$$r_d = \frac{\Delta V_f}{\Delta I_f} = \frac{\eta V_T}{I_f} + r_{\text{bulk}} \approx r_{\text{bulk}} \quad (\text{at high } I_f)$$
Solution:- As forward current \( I_f \) increases into the tens of milliamperes, \( \frac{\eta V_T}{I_f} \) becomes very small.
- The dynamic resistance approaches the small bulk resistance of the semiconductor material, typically between \( 1\text{ }\Omega \) and \( 25\text{ }\Omega \).
- The forward I-V curve becomes steep and nearly linear in this region.
Why other options are incorrect:- Option A: Dynamic resistance decreases with increasing forward current rather than approaching infinity.
- Option C: Mega-ohm resistance values occur under reverse bias, not forward bias.
- Option D: The forward dynamic resistance is a real ohmic quantity representing resistive dissipation.
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