Fermi level in semiconductors

In summary, the Fermi level is defined as a calculated parameter in the Fermi distribution. It is not necessarily the highest energy level occupied at T = 0, but rather a level where an electron cannot exist. The position of the Fermi level can be determined by calculating the probability of occupancy of states at a given temperature.
  • #1
ravi_nigam
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1. Fermi level is also defined as highest energy level at which electron can exist at 0K then it should be top of valence band but why is it in between conduction band and valence band ( in forbidden gap)? It should be in conduction band or valence band. How to explain this?

2. If density of state is 0 then no state should be there in semiconductor forbidden gap? So why we study of probability of occupancy of state in these conditions (semiconductor forbidden gap case).

3. How we calculate fermi level? Please suggest a very fundamental book; more basic than kittel
 
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  • #2
Consider the following simple example. Suppose you have just two energy levels A and B, and suppose the number of electrons present is just enough to fill the lower level A at T = 0. At some higher temperature T > 0, n electrons will be excited from A and move to B. Now where is EF? Answer: Somewhere between A and B. In fact it is half way between A and B. In this example too, EF is at an energy level where an electron cannot exist.

EF is not defined, as you claim, to be the highest level occupied at T = 0. EF is just a calculated value. It is a parameter in the Fermi distribution.
 

1. What is the Fermi level in semiconductors?

The Fermi level in semiconductors refers to the energy level at which there is a 50% chance of finding an electron. It is also known as the chemical potential and is a measure of the energy required to add or remove an electron from the material.

2. How is the Fermi level determined in semiconductors?

The Fermi level in semiconductors is determined by the material's intrinsic properties, such as the band gap and the number of electrons and holes. It is also affected by external factors such as temperature and doping concentration.

3. Why is the Fermi level important in semiconductors?

The Fermi level plays a crucial role in determining the electrical and optical properties of semiconductors. It helps to understand the behavior of electrons and holes in the material, which is essential for designing and optimizing semiconductor devices.

4. How does the Fermi level change in doped semiconductors?

In doped semiconductors, the addition of impurities introduces extra energy levels in the band structure. This affects the Fermi level, causing it to shift towards the energy level with a higher density of states. The amount and direction of the shift depend on the type and concentration of the dopant.

5. Can the Fermi level be controlled in semiconductors?

Yes, the Fermi level in semiconductors can be controlled through doping and external factors such as temperature and electric field. This allows for the manipulation of the material's electronic properties, making it possible to create different types of semiconductor devices with specific functionalities.

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