Fermi level in extrinsic semiconductors

In summary, the Fermi level in an extrinsic semiconductor remains constant after thermal equilibrium is attained. This is supported by the fact that no current should flow through any cross-section. However, this may not always be true as diffusion and drift currents can occur, causing the Fermi level to vary. Diffusion happens when there are excess carriers present, while drift occurs when an electric field is applied to guide the carriers. In both cases, the semiconductor is no longer in thermal equilibrium and the concept of invariance of Fermi level does not apply.
  • #1
prudhvi mohan
15
0
Fermi level in an extrinsic semiconductor(after attaining thermal equilibrium) is said to be invariant (constant ) , and the proof uses the fact 'no current must flow thorough any cross-section'..But I don't think its true, charge will be transported due to diffusion and this is countered by drift current( Fermi level must vary for drift to occur) ? Please tell me my mistake
 
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  • #2
diffusion happens when excess carriers are present and drift occurs when an electric field is applied that guide the carriers. If either of the situations arises, the semiconductor is no longer in thermal equilibrium and hence the concept of invariance of Fermi level is not valid.
 

FAQ: Fermi level in extrinsic semiconductors

What is the Fermi level in extrinsic semiconductors?

The Fermi level in extrinsic semiconductors is the energy level at which the probability of finding an electron is equal to 50%. It is also known as the chemical potential and is a measure of the maximum energy an electron in a semiconductor can have at a given temperature.

How does the Fermi level change in extrinsic semiconductors?

The Fermi level in extrinsic semiconductors can change depending on the type and concentration of impurities present in the material. For example, adding donor impurities will increase the Fermi level, while adding acceptor impurities will decrease it.

What is the significance of the Fermi level in extrinsic semiconductors?

The Fermi level in extrinsic semiconductors plays a crucial role in determining the electrical and optical properties of the material. It affects the concentration of free electrons and holes, which in turn, influence the conductivity and bandgap of the semiconductor.

How is the Fermi level measured in extrinsic semiconductors?

The Fermi level in extrinsic semiconductors can be measured using various techniques such as Hall effect, capacitance-voltage measurements, and optical spectroscopy. These methods rely on the manipulation of the electron concentration in the material to determine the Fermi level.

What are the factors that affect the Fermi level in extrinsic semiconductors?

The Fermi level in extrinsic semiconductors is primarily affected by temperature, impurity type and concentration, and the applied electric field. Additionally, external factors such as radiation and strain can also influence the Fermi level.

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