Why does the Fermi level shift and become disparate when metal semiconductor contact is under bias?
By simple definition ==The Fermi level E(F) is chemical potential for electrons. It is the energy level at which the probability of electron occupancy is 50%.
Supping we add a dopant to make it n-type semiconductor [ Add P to Si]. It means there is now excess of electrons .i.e.there is more electron density in whole of the bulk of such a n-type conductor.Accordingly, the Fermi Level energy is also is raised in its enegy because now the 50% of this increased electron density will be more. That is why, in n-type semiconductors,the Fermi Level enegy is raised in energy and go closer to the Concuction band of n- type conductor{See RHS of the attached figure].
Now suppose we add a dopant to make it p-type conductor[ Add B to Si]. It means that now the numbers of electrons are decreased.i.e.there is less electron density in whole of the bulk of such a p-type conductor.Accordingly, the Fermi Level energy is also decreased in its enegy because now the 50% of this decreased electron density will be less. That is why, in p-type semiconductors,the Fermi Level enegy is decreased and go closer to the Valence band of p- type conductor{See LHS of the attached figure].
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29th Jul, 2014
Abdollah Pil-ali
University of Waterloo
In metal-semiconductor contact, in thermal conductivity, the fermi-level of both side is in equal energy level, and the conduction and valence and fermi-level has been bent because of difference between the fermi-level energy of metal and semiconductor before the contact (Figure_1).
As you apply any bias to metal or semiconductor, you force the fermi-level to change, because of increasing or decreasing the energy of free electron in the last energy level.
You can see the Figure_2, for feeling of this issue.
As it is obvious, the fermi-level (in the Figure_2 the fremi-level has been shown by the electron QFL) has been changed because of applying voltage.
The simulation of metal-semiconductor has been simulated by SILVACO TCAD.
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13th Aug, 2014
Khalil Eslami Jahromi
Radboud University
So why does not happen this shift for ohmic contact under bias?
Refer to attachment
it's better to ask " what is the difference between a Schottky contact and the ohmic contact, purely from fermi level?"
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