For a P+/N junction, which of the following action would reduce the high-level injection effect?

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BlackTom AI · Accepted Answer

Question restatement: For a P+/N junction, which action would reduce the high-level injection effect?
Option 1: increase the P+ doping. Increasing the P+ doping would make the p-side more heavily doped, which can widen the depletion region on that side but does not directly address high-level injection from the n-side; in some cases it could even worsen injection by increasing built-in field asymmetry, so this choice is not the best way to reduce high-level injection.
Option 2: reduce the P+ doping. Lowering P+ doping would decrease the hole concentration on the p-side, which could alter the built-in potential and carrier dynamics, yet it does not specifically target the suppression of high-level injection from the n-side; the effect is indirect and not the primary method to mitigate high-level injection.
Option 3: increase the N doping. Doping the n-side more heavily increases the majority carrier concentration on the n-side, which reduces the relative injection of minority carriers from the n-side into the p+ region under forward bias, thereby mitigating high-level injection effects and improving carrier control.
Option 4: reduce the N doping. Lowering the N doping would reduce the electron concentration on the n-side, potentially increasing minority carrier injection or altering the injection balance unfavorably, which could exacerbate high-level injection rather than reduce it.
A deeper look: High-level injection occurs when injected minority carriers become comparable to or exceed the majority carrier supply, often under strong forward bias. In a P+/N junction, increasing the N-side doping strengthens the electron majority population, helping to suppress excessive injection of holes from the p+ side into the n-region by sharpening the built-in potential and stabilizing carrier flow. This makes high-level injection less likely. Conversely, decreasing N doping or increasing P+ doping would tend to worsen or not effectively counteract high-level injection by reducing the availability of majority carriers on the n-side or by increasing minority-carrier leakage.
Summary of reasoning: Among the options, boosting N doping directly reduces the likelihood and impact of high-level injection by enhancing the n-side’s majority-carrier reservoir and improving control over injection dynamics, whereas the other options either misalign with the mechanism or could worsen injection behavior.
Therefore, the action that would reduce the high-level injection effect is to increase the N doping.

EESM5200 (L1) Part I: Topic 7 - Real PN Junction Characteristics

For a P+/N junction, which of the following action would reduce the high-level injection effect?

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