Fermi level pinning in doped semiconductors

In summary, Fermi level pinning is a phenomenon that occurs in doped semiconductors, where the Fermi level, which is the energy level at which electrons have a 50% probability of being occupied, is pinned to a fixed position within the band gap. This is due to the presence of impurities or defects in the semiconductor material, which create energy states that trap the Fermi level and prevent it from moving freely. This pinning effect can have significant impacts on the electronic properties of semiconductors, including altering their conductivity and affecting the formation of energy barriers at junctions between different materials.
  • #1
Reid
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I am reading 'Mesoscopic electronics in Solid State Nanostructures', second edition, by Thomas Heinzel. And I find it a bit too difficult from time to time. Especielly on the concept of Fermi level pinning in doped semiconductors.

Does anyone know where to find a good explanation for this concept? Or do you know one yourself?

Thanks!
 
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  • #2
Reid said:
I am reading 'Mesoscopic electronics in Solid State Nanostructures', second edition, by Thomas Heinzel. And I find it a bit too difficult from time to time. Especielly on the concept of Fermi level pinning in doped semiconductors.

Does anyone know where to find a good explanation for this concept? Or do you know one yourself?

Thanks!

Fermi Level Pinning expresses the fact that the metal workfunction changes in magnitude when you replace SiO2 by HfSiO4 in a metal/SiO2/SC-stack, irrespective of the metal itself (material,etc). This problem disturbs the basic MOSFET-operation because of several reasons

Check out : http://academic.brooklyn.cuny.edu/physics/tung/Schottky/index.htmThe above website will teach you that in case of an interfacial region between two materials in a stack, there does not have to be charge transfer from one material to the other. This means that the Fermi Level is fixed or pinned !

This is the case when there is an insulator between the two materials like the metal/SiO2/SC stack. In that case, the Fermilevels will still align for the same reason. The potential difference over the interface equals the surface charge at the SC-surface and its image charge at the metal surface. The big question is what system generates this surface charge ? You have several models like the Metal induced Gap states where the metal wavefunctions penetrate through the interface (SiO2 layer) and they generate a certain amount of energylevels in the SC-bandgap. These energylevels (and hence the electrons occupying them) can be seen as a metal of which the Fermi level is called the charge neutrality level. Depending on the position of the SC-Fermilevel with respect to the charge neutrality level (the SC-surface-Fermi Level) the SC surface acquires the required net-charge. "required" means corresponding to lowest potential energy of the material-stack. This is just one of the several models that are out there (look at Tung's website for this). The biggest problem with this model is the fact that it does not depend on the interfacial chemistry and Tung corrected this in his socalled Bond-Polarization-model..

marlon
 
  • #3
This is great! Thank you so much. My professor couldn't answer the question! You are great! :)

The page is exactly on my level!
 

What is Fermi level pinning in doped semiconductors?

Fermi level pinning is a phenomenon that occurs in doped semiconductors where the Fermi level (the energy level at which there is a 50% probability of finding an electron) is pinned or fixed at a certain point despite changes in the doping concentration or applied electric field. This can affect the electronic properties of the material, such as its conductivity and bandgap.

How does doping affect Fermi level pinning?

Doping, which involves introducing impurities into a semiconductor, can impact Fermi level pinning by changing the concentration of available charge carriers and altering the energy levels within the material. This can lead to a shift in the Fermi level and cause it to become pinned at a specific energy level.

What causes Fermi level pinning?

The exact cause of Fermi level pinning is still a topic of debate, but it is believed to be due to the presence of surface states or defects at the interface of the doped semiconductor. These states can trap electrons and prevent them from moving freely, causing the Fermi level to become pinned.

How does Fermi level pinning affect device performance?

Fermi level pinning can have both positive and negative effects on device performance. On one hand, it can improve stability and reduce leakage currents in devices. On the other hand, it can limit the ability to tune the electronic properties of the material, which can be problematic for certain applications such as transistors and solar cells.

Can Fermi level pinning be controlled or eliminated?

While it is difficult to completely eliminate Fermi level pinning, it can be controlled to some extent by engineering the semiconductor material and its interfaces. This can involve using different types of dopants, passivating surface states, or using specialized techniques such as bandgap engineering. However, completely eliminating Fermi level pinning remains a challenge in semiconductor research.

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