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].
2 Recommendations
7th 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.
2 Recommendations
8th 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?"
8th Aug, 2014
THE Shaikh Haquemobassir Imtiyaz
Pillai Institute of Information Technology, Engineering, Media Studies and Research
@khalil sir yes there is difference in ohmic and schottky contacts
but focusing on core question lets put in simple words
fermi level or individual band level is nothing but the top level of energy so when we apply bias and combination recombination occurs the energy level shifts due to the bonded electron getting excited to free themselves and one which is free tries to shift the level under bias..so that fermi line also shifts. now which ways it shifts is upon which doping we do... and in un biased semiconductor the bend is sign of practically zero drift current or equilibrium state
Can you help by adding an answer?
Answer
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials
- Semiconductor