In case of fabricating the Metal-semiconductor contacts, we use the concepts of electron affinity and work function, where, we are normally interested in the work function of a metal and electron affinity of semiconductor.
In case of semiconductor, the work function and electron affinity w.r.t vacuum level are different, but why is there no question of electron affinity in the case of metal, where we consider only the work function.
Do the electron affinity and work function of a "metal" are similar?
Fo me, the electron affinity has a one description, does not metter is that a semiconductor or metal. It is just the difference between vacuum level and bottom of the conduction band.
Electron Affinity: https://en.wikipedia.org/wiki/Electron_affinity
For metal-semiconductor contacts more importantant is Ionization Energy: https://en.wikipedia.org/wiki/Ionization_energy
Electron affinity is defined as the change in energy (in kJ/mole) of a neutral atom (in the gaseous phase) when an electron is added to the atom to form a negative ion. In other words, the neutral atom's likelihood of gaining an electron.
Nonmetals have a greater electron affinity than metals because of their atomic structures: first, nonmetals have more valence electrons than metals do, thus it is easier for the nonmetals to gain electrons to fulfill a stable octet and secondly, the valence electron shell is closer to the nucleus, thus it is harder to remove an electron and it easier to attract electrons from other elements (especially metals). Thus, nonmetals have a higher electron affinity than metals, meaning they are more likely to gain electrons than atoms with a lower electron affinity.
Work function is defined as the minimum amount of energy required by an electron to escape from a metal surface.
@ Dmitry Vasilyev, my question is w.r.t. metal. I agree with your answer. Do you mean to say, the Fermi energy of metal is far above the conduction band edge?
Dear Indudhar Vali! Sure, Fermi energy of metal is above the conduction band edge. And if we carefully take a look at the definition of electron affinity we`ll see that not the electron affinity is important for metal-semiconductor contact. But the difference of the Fermi level in metal, Fermi level in semiconductor, and conductivity zone bottom in semiconductor. As Fermi level is the energy level with 0.5 probability to find electrons -- after building the contact the Fermi level flattens in both semiconductor and metal parts. And we are getting an energy threshold for electrons dependent on the initial difference between two Fermi levels and from the depth of Fermi level in semiconductor forbidden zone.
See for example Fig.6 at
http://www.intechopen.com/books/biomedical-engineering-technical-applications-in-medicine/implementation-of-schottky-barrier-diodes-sbd-in-standard-cmos-process-for-biomedical-applications
Dear Indudhar Vali Yes, For sure in metal Fermi energy above the conduction band edge. And I agree with explanetion of V.B. Zaytsev. That the difference is importan and I understend you can play with this difference by doping of semiconductor that shifting the Fermi energy (away from the center of the band gap if you have GaAs for example)
Dear Zaytsev and Vasilyev, Got it. thanks for your inputs.
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