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Lachlan Black

Including bulk doping when simulating QM accumulation capacitance in Schred V1

Through examination of the source code I have figured out that I need to use the “accumula=yes” flag in the “calc” section of the input file to get Schred V1 to include quantum mechanical effects when calculating the capacitance in accumulation (it is my understanding that Schred V2 does not support this feature). Inclusion of this flag results in a lower capacitance in accumulation compared to the semiclassical case, as expected. However, it also appears to result in the neglect of the bulk doping, with the capacitance minimum in depletion sitting close to zero. Is there any way around this, short of modifying the source code?

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    Gokula Kannan

    Hi lachlan, I am assuming you are simulating a MOS cap and not an SOI. I wrote the part for the Schred V2.0 and yes, you are right the V2.0 supports only 1D SWE for electrons, so it does not solve for holes in the accumulation for the MOScap. I went through the code and what i found is that the code by default solves for electrons in inversion and holes in accumulation automatically when you enable the QM mode .(it checks for the potential energy(fi) at the si-oxide interface(fi_sc) and if the value is greater than fi(end) then does the QM for electrons else if less, it does the QM for holes.(in each case the suitable PARITy bits are assigned 1,2 for electrons and holes resp., and this determined whether we solve for electrons or for holes in the QM_BODY_CHARGE subroutine) The flag for accumulate that you indicated actually enables the SOI mode of calculation and I guess thats why at zero vg you get a capacitance minimum which should be close to zero. Enabling the flag only sets flag_doping =0 which actually sets bulk doping of the gate-oxide-bulk-oxide-gate SOI structure. It does not set the bulk doping to zero,if that is what you meant.

    If you want to exclude the hole calculation in QM mode, and see how it varies with just semiclassical in accumulation in QM mode, just set the parity bit to 1 in that case as well so it does solve for electrons in inversion and solves semiclassically in accumulation.


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