## Definitions of some terms

hey guys i wanna know the definition of these terms & what are they but please i don't want big words because i won't understand i wanna understand it simply:
1-Fermi level
2-Density of states
3-Carrier concentration & the graphs (in the attachment)
4-Mass action law
5-Charge neutrality
i attached some files because i don't understand what it is saying
Attached Thumbnails

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 Do you have any chemistry background? Because the easiest way to think of the Fermi level is as your highest occupied orbital. The major difference is that in a crystal structure, your discrete atomic or molecular orbitals blend together into bands of energy levels (so it isn't a Highest Occupied Molecular Orbital, it is instead called the Fermi level). Your density of states diagram is then analogous to a molecular orbital diagram. The big difference is that you once again don't have discrete energy levels, you now have a probability distribution for possible electronic states.
 Fermi level: At zero temperature everything below is occupied, everything above is empty. At finite temperature things get smeared out a but, according to Fermi-Dirac statistics. Density of states: How many electrons can you fit at this energy? There can be occupied and unoccupied DoS, so you have to be a bit careful sometimes. Charge neutrality: Just what is says. Number of positive charges (holes and donors) = number of negative charges (electrons and acceptors) Mass action law: Read the equation. Concentration of holes times concentration of electrons is a constant. Carrier density: Number of mobile electrons that can carry an electric current. Depends on the DoS and the probability to find an electron or hole there (Fermi-Dirac statistics)