You have a P+/N junction. If you want to increase the forward bias diode current (applied voltage smaller than the built-in potential) at the same forward voltage, the most effective approach is (assuming it remains as a P+/N junction):

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Question restatement: You have a P+/N junction. If you want to increase the forward bias diode current (applied voltage smaller than the built-in potential) at the same forward voltage, the most effective approach is (assuming it remains as a P+/N junction):

Options: 1) increase N doping 2) reduce N doping 3) increase P+ doping 4) reduce P+ doping

Option 1: increase N doping. Increasing the n-side dopant concentration raises the donor density, which tends to raise the built-in potential and narrow the depletion region only under certain relationships, but in forward bias at a fixed forward voltage below the built-in potential, the higher doping generally leads to a larger barrier to injection and can reduce the forward current for the same external voltage. Additionally, higher N doping increases the equilibrium carrier concentration on the n-side, which could alter the diffusion currents, but the dominant practical effect here is an increased barrier to forward injection, making this option unlikely to increase current at the same V.

Option 2: reduce N doping. Reducing the n-side donor concentration lowers the built-in potential and broadens the depletion region, effectively easing the forward-bias injection conditions. With the same forward voltage, more carriers can be injected across the junction, increasing the forward current. This aligns with the general understanding that a smaller built-in potential and wider space-charge region (within practical limits) facilitate carrier injection under forward bias, thus increasing the current at a given V.

Option 3: increase P+ doping. Intensifying the p-side doping (making it more heavily doped) tends to raise the built-in potential and reduce the depletion width on the p-side but can also increase the difference in quasi-Fermi levels required to achieve the same forward current. In practice, the stronger doping on the p-side would not necessarily produce a larger forward current at the same forward voltage; it typically shifts the balance in a way that does not directly enhance injection efficiency under the stated condition. Therefore, this is unlikely to be the most effective approach.

Option 4: reduce P+ doping. Decreasing the p-side doping reduces the majority carrier concentration on the p-side, which can alter the diffusion currents and the barrier characteristics. However, reducing the heavily doped p-side (P+) tends to increase the depletion width and can decrease the built-in potential, but the net effect on forward current at the same forward voltage is not straightforwardly beneficial as it undermines the strong injection pathways provided by heavy p-type doping. In many practical PN junction design scenarios, this would not be the most effective route to increase forward current at a fixed V.

Summary view: The core idea is that the forward current at a given forward voltage is highly sensitive to the junction’s barrier and diffusion properties. Lowering the n-side doping reduces the barrier to electron injection from the n-side into the p-side, enhancing forward current for the same applied voltage, whereas increasing dopant levels on either side typically raises barriers or shifts carrier distributions in ways that do not straightforwardly increase current at the same V. Thus, among the options, reducing N doping is the most effective route to boost forward current at the same forward voltage for a P+/N junction.

EESM5200 (L2) Part I: Topic 6 - Carrier Actions in a PN Junction

You have a P+/N junction. If you want to increase the forward bias diode current (applied voltage smaller than the built-in potential) at the same forward voltage, the most effective approach is (assuming it remains as a P+/N junction):

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