Possibility of optical absorption by defect level in bandgap

• johsieh74326
In summary: Your Name]In summary, the activation energy of a defect level affects the probability of optical absorption of sub-bandgap photons by a semiconductor. The closer the photon energy is to the activation energy, the higher the probability of absorption. However, the photon energy and the energy difference between the defect level and the conduction band also play a role. Recommended resources for further information include books such as "Introduction to Solid State Physics" and "Fundamentals of Semiconductors: Physics and Materials Properties."
johsieh74326
Hi,

I have a tricky question regards the absorption of photons by semiconductor.

Say I got a piece of semiconductor with Eg=4eV.
Inside the bandgap, there are two defect levels, and each of them have a trapped electron.
One of the defect has the energy level that is 1eV below conduction band(so the activation energy=1eV), while the other is 2eV below the conduction band(so the activation energy=2eV).

When I apply sub-bandgap photons to this semiconductor at 3eV (larger than the activation energies for both traps), the electron in which defect will have larger chance to absorb the photons and thus jump into the conduction band?? To make it short, does the activation energy affect the possibility of optical absorption when the photon is larger than the activation energy for sure?

If there is any recommended info online I can look up regards this matter?

Thanks so much!

Hello,

Thank you for your question regarding the absorption of photons by a semiconductor with defect levels.

The activation energy of a defect level is the minimum energy required for an electron to jump from the defect level to the conduction band. In your scenario, the activation energies for the two defect levels are 1eV and 2eV, respectively. When a photon with energy greater than 3eV is applied to the semiconductor, it is possible for both defect levels to absorb the photon and release the trapped electrons into the conduction band. However, the probability of this happening is determined by the energy difference between the defect level and the conduction band.

In general, the closer the energy of the photon is to the activation energy of a defect level, the higher the probability of absorption by that defect level. In your case, since the photon energy is 3eV and both defect levels have activation energies lower than 3eV, both defects have a chance of absorbing the photon and releasing their trapped electrons into the conduction band. However, the defect level with the lower activation energy (1eV) will have a higher probability of absorption compared to the defect level with the higher activation energy (2eV).

To answer your question, the activation energy does affect the possibility of optical absorption, but it is not a determining factor. The probability of absorption also depends on the energy of the photon and the energy difference between the defect level and the conduction band.

As for recommended information, there are many online resources available that discuss the absorption of photons by semiconductors and the role of defect levels. Some recommended resources include:

1. "Introduction to Solid State Physics" by Charles Kittel
2. "Semiconductor Optoelectronic Devices" by Pallab Bhattacharya
3. "Fundamentals of Semiconductors: Physics and Materials Properties" by Peter Y. Yu and Manuel Cardona

I hope this helps answer your question. Please let me know if you have any further inquiries.

1. What is the "defect level" in a bandgap?

The defect level in a bandgap refers to a location in the energy band structure of a material where there is an electronic state that is neither fully occupied nor fully empty. This defect state can be caused by impurities, vacancies, or structural defects in the material.

2. How does the presence of defect levels affect optical absorption?

When a material has defect levels within its bandgap, it can absorb light at specific wavelengths, which would not be possible in a perfect, defect-free material. This is because the defect levels act as intermediate energy states that can facilitate the absorption of photons by electrons.

3. Is it possible for defect levels to enhance optical absorption in a material?

Yes, it is possible for defect levels to enhance optical absorption in a material. This is because the presence of defect levels can increase the number of available electronic states, thereby increasing the probability of light absorption by the material.

4. Can defect levels lead to changes in the color of a material?

Yes, the presence of defect levels in a material can lead to changes in its color. This is because the absorption of specific wavelengths of light by the defect levels can cause certain colors to be reflected, giving the material a different color appearance.

5. How do scientists study the possibility of optical absorption by defect levels in a material?

Scientists study the possibility of optical absorption by defect levels by using various analytical techniques such as absorption spectroscopy, photoluminescence spectroscopy, and electrical measurements. These techniques allow for the characterization and quantification of defect levels in a material and their impact on optical absorption.

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