Relaxation/Polarization with Semiconductor Electrons

In summary, when an electron fills the last empty state in the valence band of an n-type semiconductor, it prevents other valence electrons from reducing their energy through the process of polarization and relaxation around the impurity center. This can only occur when there is an available hole at the top of the valence band, allowing the remaining electrons to form stronger bonds with the impurity and lower their energy.
  • #1
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Please help me understand the following (general) statement, referring to electrons in a full valence band of an n-type semiconductor:

"An electron filling up the last empty state in the valence band will in doing so prevent the other valence electrons from reducing their energy through polarization and relaxation around the impurity center"

I don't understand what is meant by the last part of this. I know that in a full band, electrons have no empty state to move into, but I don't know what is meant by polarization and relaxation "around the impurity."

The impurity referred to is a donor (n-type SC). Another statement (which I think is basically the same) says:

"In the case of a completely filled valence band, no (impurity, I assume) scattering can take place, because all states are occupied. Now, if a hole is created at, for example, the top of the valence band, the remaining valence electrons will relax around the impurity ions... this new flexibility of the system makes the system lower in its energy."

What does this mean "relax around impurity ions"?

To sum it up, what I'm not understanding here is:

a) what is meant by "relax around the impurity" (I have no idea what they mean by "relax"), and

b) reducing energy by polarization or relaxation (What/how/why? What do they mean by polarization?)
 
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  • #2
Relaxation around the impurity refers to the process by which the remaining valence electrons can move closer to the impurity ion to form a stronger bond. This is known as "polarization" and it allows the electrons to reduce their energy through the formation of stronger bonds with the impurity. When the valence band is full, no polarization can take place because all states are occupied, so the electrons cannot reduce their energy by forming stronger bonds with the impurity. However, if a hole is created at the top of the valence band, this gives the remaining valence electrons the flexibility to move closer to the impurity to form stronger bonds, thus reducing their energy.
 

1. What is relaxation/polarization with semiconductor electrons?

Relaxation and polarization refer to two processes that occur in semiconductors when electrons are excited from their ground state to a higher energy state. Relaxation is the process by which these excited electrons return to their ground state, releasing energy in the form of light or heat. Polarization, on the other hand, is the redistribution of charges in the semiconductor due to the presence of the excited electrons.

2. How do relaxation and polarization affect the behavior of semiconductors?

Relaxation and polarization are important phenomena in semiconductors, as they can significantly influence the electrical and optical properties of these materials. Relaxation can lead to the emission of light, which is crucial in the operation of devices such as LEDs and lasers. Polarization can alter the conductivity and refractive index of semiconductors, making them useful in devices like transistors and solar cells.

3. What factors influence the relaxation and polarization processes in semiconductors?

Several factors can affect the relaxation and polarization processes in semiconductors. These include the bandgap energy, temperature, and the presence of impurities or defects in the material. Additionally, the type of semiconductor (e.g. n-type or p-type) and the applied electric field can also impact the relaxation and polarization behaviors.

4. How are relaxation and polarization measured in semiconductors?

There are various experimental techniques used to measure the relaxation and polarization processes in semiconductors. These include time-resolved spectroscopy, which tracks the emission of light from the excited electrons, and capacitance-voltage measurements, which can detect changes in the electrical properties of the material due to polarization. Other methods include transient photocurrent and electroreflectance spectroscopy.

5. What are the practical applications of relaxation and polarization in semiconductors?

The relaxation and polarization processes in semiconductors have numerous practical applications, particularly in the field of optoelectronics. As mentioned, relaxation is essential in the operation of light-emitting devices, while polarization is crucial in the development of advanced photonic devices, such as modulators, switches, and detectors. Additionally, the ability to control and manipulate relaxation and polarization in semiconductors has led to advancements in fields like telecommunications, imaging, and renewable energy.

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