Difference between fermi energy level in metals and semiconductors [duplicate]

It is not exactly a question its a kind of confusion ... Here my confusion starts... what is meant by Fermi energy level?? The only definition that i found was the energy level at which the probability of finding of electron is 50%..

First question is whether this definition applicable to all the materials or only for metals or only for semiconductors?? But in semi conductors the Fermi energy level is in mid of the valency band and the conduction band...

So my second question was in semi conductors whether the Fermi energy level is the maximum energy that the electron in that material is having or it is a particular energy that 50% of the electrons are having the energy more than that level ??

sorry if i am messing up the topic i am keeping all the confusions that are having in my mind in to words.

Last question was in if electron is in the highest energy level of the conduction band what does it mean ?? electron is having the energy only equal to the energy level????

• Possible duplicates: physics.stackexchange.com/q/30922/2451 and links therein. – Qmechanic Jun 27 '16 at 17:00
• I didn't get the answer by seeing the question that was linked above as a duplicate... it will help me a lot if you answer at least yes or no for all the above three questions individually.... – Suneeldatta Kolipakula Jun 28 '16 at 3:06

That definition of the Fermi level is applicable to all materials. However, I believe you'll find it a lot clearer once you understand that the Fermi level is in fact the energy level at which the probability of an electron state being occupied is 50%.

In a semiconductor, the Fermi level is indeed in the forbidden band, however there are no available states in the forbidden band. Therefore, even though the probability of an electron state being occupied is 50%, there are no electrons present in the bandgap (0.5*0=0).

It is very incorrect to say that 50% of the electrons have energy above the Fermi level. While it is certainly possible if you have an incredibly skewed distribution of electron states, this is not true for most materials.

The area under the graph before the Fermi level is clearly much larger than the area after it.

I'm afraid I don't quite understand your last question.

• Hey it makes me a bit clear.. What i mean to say in the last question was acording to paulis principle no two electrons will have all 4 quantum numbers same..So all the ele in valency band will have diff energy levels right..So one electron among all the electrons which are there in the valency band will have the highest energy right... so when we expose the substance to external energy the electron which is in the highest energy level of the valency band will move to conduction band am i right??? – Suneeldatta Kolipakula Dec 27 '16 at 10:05
• ..continuation for above comment....so when we expose the substance to external energy in such a way that the exposed energy is exactly equal to the energy diff between highest energy level of valency band and lowest energy level of conduction band..the electron which is in the highest energy level of the valency band alone will move to conduction band am i right??? – Suneeldatta Kolipakula Dec 27 '16 at 10:15
• strictly speaking, if you were to have a photon with exactly the same energy as the difference between the highest occupied state in the valence band and the lowest unoccupied state in the conduction band, it would "move" the electron at the highest occupied state in the valence band to the conduction band. while this is true, I cannot imagine a scenario in which you would deal with the excitation of a single electron in that manner – Dr Coconut Jan 2 '17 at 8:48
• Thanks for you answer!!! There is no real time scenerio such.. I just want to know whether my assumption is correct or not. – Suneeldatta Kolipakula Mar 13 '17 at 10:12