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

Here we are considering a P+/N junction where both sides are effectively shorted, and we want to know which modification will produce the largest increase in current when the diode remains a short after the change.

Option 1: increase the P+ region length
- Expanding the P+ region length increases the physical area of the heavily doped contact on the p-side. In a practical shorted path, larger contact area can reduce contact resistance somewhat, which might allow a bit more current. However, since the device is already a short, the dominant limitation often lies in the series path resistance and the far-from-ideal aspects of the junction, not just the contact area. The net effect is typically modest and unlikely to produce the largest increase in current compared with changes that shorten the conductive path itself.

Option 2: reduce the P+ region length
- Reducing the P+ length decreases the conductive cross-section on the p-side, which tends to increase the path resistance. In a shorted configuration, this would generally reduce current, not increase it. Therefore this change would not lead to a higher current and is unlikely to be beneficial for increasing the current.

Option 3: increase the N region length
- Lengthening the N region makes the current path longer, increasing the series resistance of the path from one contact to the other. In a shorted junction, this tends to hinder current flow and reduce current, rather than enhance it. So this change would not maximize current increase.

Option 4: reduce the N region length
- Shortening the N region reduces the length of the conductive path through the n-type material. With a shorter path, the series resistance drops, allowing more current to flow for the same applied voltage. Among the options, this change most directly lowers the path resistance and is the most effective at increasing current in a shorted P+/N junction.

Across all options, the modification that lowers the primary resistance in the conduction path typically yields the largest gain in current. Reducing the N region length directly reduces the path resistance, making it the strongest contributor to increasing current in this setup.

EESM5200 (L2) 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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