Conceptual question about current flow and transmission spectrum

[Arya]

Hi All,

Greetings !

I was thinking from a circuits perspective into quantum simulations. I wish to know, when happens when a perfect device and a leaky device are connected in series and both of them are OFF.

Lets say we have a perfect semiconducting GNR (say GNR A). To see how good a transistor it would make I calculate the transmission spectrum and find two lobes up and below fermi level with appropriate bandgap in between. This device would be perfectly OFF i.e. ideally zero leakage current without gate bias.

Now consider a GNR B with defects such that the transmission spectrum now has no or very little bandgap. This device will leak considerably more than GNR A. If I connect both devices A and B in  series in a circuit. I would expect ideally no current to flow since device A is strongly cut off and is in series.

If I generalize this observation to a large GNR in Z direction. Then I can conceptually divide it into small devices in series and so long as any one of those device is perfect I would expect any number of defects in neighbouring devices will not not cause the big device to leak since we have at least one sub-transistor that is perfectly off. We know this doesn't happen a GNR with LER leaks (even though it might have perfect regions between two defects). Where is the fallacy in my reasoning?

Thanks,
-Arya

[Dipankar Saha]

In first case...one of the transistor is providing comparatively much higher resistance...thus restricting the current to flow through the path which is actually made of the series connection of one high and one low resistance transistor......

For the other case, when a single device is conceptually divided into to separate regions,  then the entire resistance provided by the device can be computed taking into the effects of the adjacent atomic orbitals..... Now even if there is one part which is perfect (Would have provided a fair amount of  BG), still the neighboring sites which are having LER will have a strong impact on determining the overall band structure of the device....thus ultimately the BG would be shifted to any lower value..... So in the end the effective resistance of the device will get very much altered only.... Thereby, I think, this case is quite different from the first one....