Significance Of Fermi Level in Semiconductor

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I understood that the fermi level is a hypothetical energy level given by the Fermi-Dirac distribution where the probability of finding an electron is exactly 50%. My question is: it always takes (Ec-Ev) energy to excite the electrons in the conduction band in an intrinsic semiconductor or (Ec-Ed), (Ec-Ea) for extrinsic semiconductors then what is the usefulness of knowing the Fermi level in the semiconductor? Why can't we do without the Fermi level.
 

Simon Bridge

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Look at InAs-GaSb junction. Here you have a confined electron and hole gasses very close to each other.
iirc. The electron and hole states are filled to the fermi level on both sides of the junction.

Mostly it is a useful benchmark to compare things with - useful when designing and modelling semiconductor devices.
 
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I understood that the fermi level is a hypothetical energy level given by the Fermi-Dirac distribution where the probability of finding an electron is exactly 50%. My question is: it always takes (Ec-Ev) energy to excite the electrons in the conduction band in an intrinsic semiconductor or (Ec-Ed), (Ec-Ea) for extrinsic semiconductors then what is the usefulness of knowing the Fermi level in the semiconductor? Why can't we do without the Fermi level.
As an example when you connect a N-type semiconductor to a p-type one (with less Fermi energy), the carriers would move from one to another until their Fermi level become the same.You can read semiconductor device books to see further applications of Fermi energy.
 
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Thanks for your replies!!
 

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