Concept:High-level injection occurs when the density of injected minority carriers exceeds the background doping concentration of the drift region. To maintain charge neutrality, majority carrier density rises to match, drastically lowering the drift region's resistance (conductivity modulation).
Formula:$$\Delta n = \Delta p \gg N_D \implies \sigma = q (n \mu_n + p \mu_p) \gg \sigma_0$$
Solution:- Under high forward currents, large numbers of electrons and holes are injected into the lightly doped drift region.
- This increases the total mobile carrier density well above the background doping level, reducing the dynamic series resistance of the diode and enabling high current conduction with low forward voltage drop.
Why other options are incorrect:- Option A: Dopant atoms remain fixed in the crystal lattice.
- Option B: The physical dimensions of the semiconductor chip remain unchanged.
- Option D: Conductivity modulation is an ambipolar carrier injection effect, not superconductivity.
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