In semiconductor material, the distance between conduction band and vacuum level defined as electron affinity. In some cases, position of conduction band may vary from vacuum point, or conduction band reduced. As a result, the value of electron affinity increases. What are the main reasons for moving conduction band, not valence band? and why electron affinity varies?
I guess your interesting question is related to the Anderson rule, Dear Adnan Hosen.
Anderson's rule * is based on the use of electron affinity - which is the energy required to transfer an electron from the bottom of the conduction band Ec into the vacuum, where it can leave the material.
The electron affinity is practically independent of the position of the Fermi level which depends on doping (in contrast to the work function, which is measured from the Fermi energy and therefore depends significantly on the degree of doping).
* https://en.wikipedia.org/wiki/Anderson%27s_rule
Dear Pedro L. Contreras E. , thank you so much sir for reaching to me out. Your valuable feedback will really get help that I work for.
Anderson's rule basically deals with band alignment and band offsets, and the relative position for both valence band and conduction bands are unknown at instant. How actually vary the relative distance between conduction band and vacuum level?
You are welcome, Dear Adnan Hosen.
I understand that according to Anderson's rule when considering the band struct, the level of the minimum energy (in this case from the bottom of the conduction band) is taken as a common reference point for the electron energy in a vacuum, from which the electron affinity is subtracted.
So my answer to your question is, if we vary the gap Eg, the relative distance between the conduction band and vacuum level is changed.
Let us show it in one diagram, for a n dopped type, because without an energy band diagram is very hard :)
Dear Adnan Hosen ,
The electron affinity of a material is the energy that an electron looses when it is transferred from the vacuum free electron level to the bottom level in the conduction band. It is a material characteristics and therefore it changes from one material to the other one. The change dates back to the electronic structures of the constituting atoms and their assembly in form of solid materials.
Even the ability of atoms to accept electrons is also called the electron affinity of atoms. This naturally changes from one atom to the other because the atoms of different materials have their unique electron structure.
Best wishes
While the work function of a semiconductor can be changed by doping, the electron affinity ideally does not change with doping and so it is closer to being a material constant. However, like work function the electron affinity does depend on the surface termination (crystal face, surface chemistry, etc.) https://en.m.wikipedia.org/wiki/Electron_affinity
Check https://www.sciencedirect.com/topics/earth-and-planetary-sciences/electron-affinity
Hello Hosen,
Kindly look at this paper
http://www.jiwaji.edu/pdf/ecourse/physics/Semiconductor-Band%20Structure.pdf
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