Anonymous
Oct 10
Carrier concentration, Fermi level, and conductivity of extrinsic semiconductors.
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Oct 10
Extrinsic semiconductors are doped semiconductors where impurities are intentionally added to the crystal lattice to increase the carrier concentration. The two main types of extrinsic semiconductors are n-type and p-type, depending on the type of impurity added.
In n-type extrinsic semiconductors, donor impurities such as phosphorus or arsenic are added to the crystal lattice, which introduces extra electrons into the conduction band. This increases the carrier concentration of electrons in the material. The Fermi level in n-type semiconductors is closer to the conduction band, as there are more electrons available for conduction.
In p-type extrinsic semiconductors, acceptor impurities such as boron or gallium are added to the crystal lattice, which creates holes in the valence band. This increases the carrier concentration of holes in the material. The Fermi level in p-type semiconductors is closer to the valence band, as there are more holes available for conduction.
The conductivity of extrinsic semiconductors is determined by the carrier concentration and mobility of the carriers. The higher the carrier concentration, the higher the conductivity of the material. The mobility of carriers also plays a role in determining the conductivity, as it affects how easily the carriers can move through the material.
Overall, extrinsic semiconductors have higher carrier concentrations and conductivities compared to intrinsic semiconductors, making them more suitable for use in electronic devices such as transistors and diodes.
In n-type extrinsic semiconductors, donor impurities such as phosphorus or arsenic are added to the crystal lattice, which introduces extra electrons into the conduction band. This increases the carrier concentration of electrons in the material. The Fermi level in n-type semiconductors is closer to the conduction band, as there are more electrons available for conduction.
In p-type extrinsic semiconductors, acceptor impurities such as boron or gallium are added to the crystal lattice, which creates holes in the valence band. This increases the carrier concentration of holes in the material. The Fermi level in p-type semiconductors is closer to the valence band, as there are more holes available for conduction.
The conductivity of extrinsic semiconductors is determined by the carrier concentration and mobility of the carriers. The higher the carrier concentration, the higher the conductivity of the material. The mobility of carriers also plays a role in determining the conductivity, as it affects how easily the carriers can move through the material.
Overall, extrinsic semiconductors have higher carrier concentrations and conductivities compared to intrinsic semiconductors, making them more suitable for use in electronic devices such as transistors and diodes.
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Google Gemini AI
Oct 10
Carrier Concentration in Extrinsic Semiconductors
In extrinsic semiconductors, doping introduces additional mobile charge carriers. For n-type semiconductors (doped with electron donors), the carrier concentration (n) is given by:
```
n ≈ N_d
```
where N_d is the concentration of donor atoms.
For p-type semiconductors (doped with electron acceptors), the carrier concentration (p) is given by:
```
p ≈ N_a
```
where N_a is the concentration of acceptor atoms.
Fermi Level
The Fermi level (E_F) is the energy level at which the probability of finding an electron is 50%. In extrinsic semiconductors, the Fermi level shifts from its intrinsic position (E_i) based on the doping type and concentration.
For n-type semiconductors:
```
E_F > E_i
```
For p-type semiconductors:
```
E_F < E_i
```
Conductivity of Extrinsic Semiconductors
The conductivity (σ) of an extrinsic semiconductor is determined by the number and mobility of charge carriers. For n-type semiconductors, the conductivity is given by:
```
σ = n - e - μ_n
```
where e is the electron charge and μ_n is the electron mobility.
For p-type semiconductors, the conductivity is given by:
```
σ = p - e - μ_p
```
where μ_p is the hole mobility.
Effects of Doping on Conductivity
Doping generally increases the conductivity of a semiconductor because it introduces additional mobile charge carriers. However, the conductivity depends on the type and level of doping.
- N-type semiconductors: Higher N_d leads to higher electron concentration and thus higher conductivity.
- P-type semiconductors: Higher N_a leads to higher hole concentration and thus higher conductivity.
In extrinsic semiconductors, doping introduces additional mobile charge carriers. For n-type semiconductors (doped with electron donors), the carrier concentration (n) is given by:
```
n ≈ N_d
```
where N_d is the concentration of donor atoms.
For p-type semiconductors (doped with electron acceptors), the carrier concentration (p) is given by:
```
p ≈ N_a
```
where N_a is the concentration of acceptor atoms.
Fermi Level
The Fermi level (E_F) is the energy level at which the probability of finding an electron is 50%. In extrinsic semiconductors, the Fermi level shifts from its intrinsic position (E_i) based on the doping type and concentration.
For n-type semiconductors:
```
E_F > E_i
```
For p-type semiconductors:
```
E_F < E_i
```
Conductivity of Extrinsic Semiconductors
The conductivity (σ) of an extrinsic semiconductor is determined by the number and mobility of charge carriers. For n-type semiconductors, the conductivity is given by:
```
σ = n - e - μ_n
```
where e is the electron charge and μ_n is the electron mobility.
For p-type semiconductors, the conductivity is given by:
```
σ = p - e - μ_p
```
where μ_p is the hole mobility.
Effects of Doping on Conductivity
Doping generally increases the conductivity of a semiconductor because it introduces additional mobile charge carriers. However, the conductivity depends on the type and level of doping.
- N-type semiconductors: Higher N_d leads to higher electron concentration and thus higher conductivity.
- P-type semiconductors: Higher N_a leads to higher hole concentration and thus higher conductivity.
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