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I have the following problem:

enter image description here

I want to find the graphical current/voltage relationship for both the MOSFETs on the left. The only difference I can actually spot is the doping of the body of the MOSFETs. There's a slight increase in acceptor dopants in the MOSFET below. I'm not too sure how this would affect the graph. Any suggestions?

For the first MOSFET (with p-), I think we'll get a rough sketch of:

enter image description here

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Your plot is (qualitatively) valid in the near subthreshold region, VGS < Vth.

The threshold voltage depends on the acceptor concentration in the substrate. For a heavier doped substrate, the threshold voltage Vth of an n-type mosfet is higher. The current voltage formula for VDS ≥ (VGS – Vth) and VGS < Vth is $$ i_D ≈ I_{D0}·exp\left({-{κ·(V_{th}-V_{GS}) - V_{BS})}\over{V_T}}\right) $$ where VGS is the gate/source potential, VBS is the substrate (bulk/source) potential, κ is a "capacitance channel divider" coefficient Cox/(Cox + CD), CD is the depletion layer capacitance.

In principle, the depletion layer capacitance depends on the channel's acceptor concentration, so the subthreshold slope also changes. Pay attention: for a "classical" transistor layout (not tunneling, 3D nanowire or else) it is greater than 60 mV even with a lightly doped substrate, still more for a heavier doped substrate case.

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