Hi all,
As we all know that graphene complex conductivity can be tuned by changing the chemical potential or Fermi energy level. My concern is that if there is a max value of chemical potential in practical way?
It is said that 0.6 eV is the limitation from some scientists. However, there are a lot of papers based on graphene with chemical potential more than 1.5 eV. How do you think about this ?
Look forward to your comments and suggestions.
Thank you in advance.
Bin
Dear Bin Zhang,
The chemical potential of anything, far away from the surfaces, where there exists charge neutrality, can be calculated directly from Fermi-Dirac statistics, given all the relevant quantum mechanical energy levels of the system. So, give me the electron band structure of your graphene and I will tell you what is its chemical potential. In usual semiconductors, like Silicon, it is usually sufficient (in absence of shallow and deep dopant/defect levels in the gap) to consider only two levels , top of the valence band and the bottom of the conduction band.
Specifically to your question:
1. To say that chemical potential is 0.6 eV is wrong. This quantity is energy difference and therefore you have to specify 0.6 eV relative to WHAT reference energy.
2. As stated above, the parameters, determining the value of the chemical potential are the electron energy levels, so it seems to me that there is no consensus regarding the electron energy band structure in this material . On the other hand the chemical potential in Silicon can be moved through shallow doping from almost zero to the value of tghe electron energy gap ~1.2 eV. relative to the edge(top) of the valence band .
i hope this will help you a bit
With best regards
Petr
Dear Bin and Ali,
I do not agree with Ali, in general, there is NO limitation on the applied field across a semiconductor and/or insulator (the same goes even for metals !). Well, there is a dielectric breakdown voltage which means that at that voltage (NOTHING to do with contacts), your materials gets destroyed.
The existence of dipole layer -> voltage drop across the interface electrode/graphene is the result of the difference in the electrochemical potential across the inteface and has nothing to do with an applied field, it is there at thermal equilibrium, with no ecternal field applied.
So, I still do not understand at all what limitation is one talking about. The only possible effect of the interfaces could be envisaged in case that the graphene layer is extraordinary thin, so that the interface regions are larger than the thickness of the layer(graphene) in question.
With best regards
Petr
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