Assume you have a P+/N junction that both the P+ side and the N side are short. Which of the following change (which assume the diode remains as a short P+/N diode after the change) will lead to the highest increase in current

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BlackTom AI · Accepted Answer

When analyzing a P+/N junction that is effectively shorted (the diode behaves like a short circuit across the junction), the current is primarily governed by the series resistance along the current path through the doped regions. Changing the physical length of the conducting regions changes this series resistance.

Option 1: increase the P+ region length. Making the heavily doped P+ side longer increases the distance the current must travel through that region, thereby increasing the series resistance of the path and reducing the current. This would not lead to the highest increase in current; in fact, it would tend to decrease it.

Option 2: reduce the P+ region length. Shortening the P+ region reduces some portion of the path length and its associated resistance, which could allow a bit more current, but the impact is limited compared to changes on the N side if the N region provides a substantial portion of the resistance. The effect is not as dominant as altering the N region length.

Option 3: increase the N region length. Extending the N region length increases the path length through a portion of the junction that carries current, raising the resistance and thus lowering the current. This change works against increasing current, so it would not yield the highest current increase.

Option 4: reduce the N region length. Shortening the N region directly shortens the current path through a region that contributes to the series resistance. This reduces overall resistance more effectively, permitting a larger increase in current when the diode is treated as a short. Consequently, this change is the one most likely to maximize current flow in the shorted configuration.

Across all options, the dominant factor is how the path length (and therefore the series resistance) changes. Reducing the length of the N region minimizes the series resistance along the current path the most, leading to the greatest potential increase in current. The other options either increase path length or alter a portion of the path in ways that do not promote as large a rise in current.

EESM5200 (L1) Part I: Topic 6 - Carrier Actions in a PN Junction

Assume you have a P+/N junction that both the P+ side and the N side are short. Which of the following change (which assume the diode remains as a short P+/N diode after the change) will lead to the highest increase in current

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