QuantumATK Forum
QuantumATK => General Questions and Answers => Topic started by: Dipankar Saha on June 21, 2016, 08:36
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Hi,
Is there at all any effect of spatial region (metal/dielectric)... on the calculations of electrode extension part?
Best_
Dipankar
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Yes, metallic/dielectric spatial regions have the exact same effect on the electrode extension as on the scattering region. In fact, also on the electrodes, if your spatial region(s) are also present there.
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Is that true...(Specially, when one of the electrodes.. is made of S.C. extension)?!! / When we apply gate voltage to modulate the barrier..., the electrode extnsn. region retains the intrinsic S. C. band alignment..../ The effect of gate voltage can be only seen... for the rest of the channel region (or, scattering region in other words)...
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No, the potential and electron density is computed fully self-consistently in the entire central region, incl. the electrode extensions. They are only required to match the electrode by geometry, basically for technical reasons, but can have a different electron structure than the corresponding electrode atoms. Of course, in reality you want that this region is very close to bulk-like, but it's not a strict requirement.
Of course, this also points to the fact that in order to have proper convergence and a good physics picture, if you place a gate in the electrode extensions, it should also be present in the electrodes, for consistency. But this is a choice, in terms of the device design. If you want a gate that covers the whole region from source to drain, then you also include it in the electrodes. Otherwise (and typically) you only have a gate in the middle of the scattering region, and enough screening material outside. Compare for instance the device here:
http://quantumwise.com/documents/tutorials/latest/InAsDevice/index.html/chap.nanowiredevice.html#sect2.nanowiredevice.setup.gate
A common mistake people make is to make the central region too short...
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Thank you very much Anders for all the details.... :)
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In this regard, I wanted to ask :
Whenever we define a metallic region (say, gate contact), we just mention the voltage associated with that. But, isn't it reqd. to characterize the gate contact by W.F. ??!! (Specially, when I'm looking for band alignments...)
Best_
Dipankar
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Yes it is. See http://quantumwise.com/documents/tutorials/latest/InAsDevice/index.html/chap.levels.html