What affects electron mobility in semiconductors and metals?

In summary, the conversation discusses the difference in mobility of electrons in semiconductors and metals. It is explained that the mobility is essentially a measure of how often carriers scatter and that in semiconductors, the low intrinsic carrier concentration results in less scattering and therefore higher mobility. In contrast, metals have a higher carrier density and therefore a lower mobility. The possibility of electron-electron interaction as a factor is also mentioned, but it is argued that this is not likely due to the low interaction in metals. The conversation ends with a question about the potential difference in phonon population between semiconductors and metals.
  • #1
Chiz
4
0
Hi there,

i've got a question about the mobility of the electrons in semiconductors and metalls.
in a semiconductor the mobilities are ~ 1000 cm²/Vs. In metals the mobilities are in the range of 50 cm²/Vs. what's the origin of that great difference?
 
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  • #2


Physically, carriers will accelerate in an applied field until they scatter off of some obstacle, at which point they start to accelerate again and end up having some average velocity (drift velocity) when acted on by the field. The mobility relates this velocity to the magnitude of the field, so its essentially a measure of how often carriers scatter. I think the reason that semiconductors have such high mobility is because the intrinsic carrier concentration is so low that electrons don't scatter off of each other. As the figure below shows, at high doping levels the carrier density approaches that of a metal, and the mobility drops down towards that 50 cm2/Vs value that you mentioned.

mobility_doping4.png
 
  • #3


But in metals the electron-electron interaction is very small because of the pauli principle. that's explained in the book of Ibach and Lüth "Solid state physics". there's written that you can neglect that effect and can treat the electrons as non-interacting particles. so in my opinion the electron electron interaction can't be the reason for that great difference in the mobilities.
 
  • #4


hmm ok it was just a guess which seemed slightly plausible. Is there any difference in the phonon population of semiconductors and metals?
Let me know if you come up with anything, I'm also interested in this question.
 

1. What is the mobility of electrons?

The mobility of electrons refers to the ability of electrons to move through a material in response to an electric field. It is a measure of how easily electrons can move within a material.

2. How is the mobility of electrons measured?

The mobility of electrons is typically measured in units of square centimeters per volt-second (cm^2/Vs). It can be measured experimentally using techniques such as Hall effect measurements or by calculating the drift velocity of electrons in a material.

3. What factors affect the mobility of electrons?

The mobility of electrons can be affected by several factors, including the type of material, temperature, impurities in the material, and the strength of the applied electric field. In general, higher temperatures and higher concentrations of impurities can decrease the mobility of electrons.

4. Why is the mobility of electrons important?

The mobility of electrons is an important factor in the performance of electronic devices. Higher mobility allows for faster movement of electrons, resulting in faster and more efficient electronic devices. It is also a key factor in determining the conductivity of a material.

5. How does the mobility of electrons differ in different materials?

The mobility of electrons can vary greatly between different materials. Metals, for example, typically have high electron mobility due to their free electron structure, while insulators have very low mobility. Semiconductors have intermediate mobility and can be modified through doping to increase or decrease the mobility of electrons.

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