nnp:mosfet_in_2d
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nnp:mosfet_in_2d [2020/08/03 14:53] daryoush.nosraty-alamdary [Comparison of Different Mobility Models] |
nnp:mosfet_in_2d [2024/01/03 16:01] stefan.birner removed |
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| </caption> | </caption> | ||
| </figure> | </figure> | ||
| + | As we can see there is clearly two different quantum confined modes in the inversion layer of the channel for this MOSFET. | ||
| - | In the above input characteristics curve, however, the drift and diffusion parts are hard to distinguish from each other without the logarithmic scale. | ||
| - | This could be enhanced using a ''shift'' parameter in the ohmic contact of the drain: | ||
| - | <code> | ||
| - | ohmic{ | ||
| - | name = Drain_Contact | ||
| - | shift = 0.40 # [eV] used to increase (or decrease) | ||
| - | # the resistivity of the ohmic contact | ||
| - | bias = $SourceDrainVoltage | ||
| - | } | ||
| - | </code> | ||
| - | Basically the shift of the band structure using the shift parameter in the ohmic contact leads to the change of the resistivity of the ohmic contact (see [[https://www.nextnano.de/nextnanoplus/software_documentation/input_file/contacts.htm|contacts{}]]). | + | With regards to the issue of convergence for the output characteristics, the convergence parameters become very relevant, since for the wrong set of parameters, the simulations may very well never converge and if so might take a significant amount of time. The key parameter to keep in mind is the ''alpha_fermi'' parameter in [[https://www.nextnano.com/nextnanoplus/software_documentation/input_file/run.htm | current-poisson{}]] calculations, which would decide the fate of the calculations. This parameter needs to be chosen corrently, and also since it will be dynamically reduced, the //alpha_scale// parameter also need to be set appropriately, with a relatively small //alpha_iterations// (default is 1000, which is very high!!!), so that a quick adjustment can be achieved if the parameter is too large. One also needs to significantly increase the number of iterations from the default 100, to a few thousand. This so called under-relaxation parameter for the quasi-Fermi level is important due to the fact that it decides the volume of the search for the solutions. |
| - | This has the advantage of bringing the I-V curve into a better form, distinguishing the drift and diffusion even without the logarithmic scale, and therefore consequently, making the determination of the threshold voltage $V_{\rm Th}$ easier. | + | |
| - | However the price to pay is that the output current will be significantly less in terms of [A/cm] (in our case close to 1 order of magnitude less). | + | |
| - | Without the shift in the drain contact the input I-V characteristics look somewhat differently, as shown in figure {{ref>fig7}}: | + | |
| - | + | ||
| - | <figure fig7> | + | |
| - | {{ :nnp:modelocking.gif?550 |}} | + | |
| - | <caption> ** The input characteristics of the N-Ch MOSFET calculated classically with the Masetti mobility, both in normal and logarithmic scales, without the effect of the shift of the ohmic drain contact. ** | + | |
| - | </caption> | + | |
| - | </figure> | + | |
| - | + | ||
| - | With regards to the issue of convergence for the output characteristics, relevant, since for the wrong set of parameters, the simulations may very well never converge and if so might take a significant amount of time. | + | |
| - | The key parameter to keep in mind is the ''alpha_fermi'' parameter in [[https://www.nextnano.com/nextnanoplus/software_documentation/input_file/run.htm | current-poisson{}]] calculations, which would decide the fate of the calculations. | + | |
| - | One also needs to significantly increase the number of iterations from the default 100, to a few thousand. | + | |
| - | This so called under-relaxation parameter for the quasi-Fermi level is important due to the fact that it decides the volume of the search for the solutions. | + | |
| If the solution somehow is located outside of this volume | If the solution somehow is located outside of this volume | ||
| - | ------------------ | ||
| - | |||
| - | f | ||
| - | |||
| - | -------------------- | ||
| - | |||
| - | |||
| - | --------(In development)------ | ||
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