How can one measure density of states?

• afrano
In summary: I was not suggesting going as far as looking at the distribution of occupancies in reciprocal space. I was merely suggesting using photoelectron spectroscopy to get the occupancy at a particular energy which means I don't have to use ARPES. Traditional photoelectron spectroscopy will not tell you anything about the band structure, but it will give you information about the occupied energy levels.
afrano
Hello, folks.

Q: How can one measure the density of states of a semiconductor and a conductor? I would imagine you want to measure the charge carrier density and then you can calculate the density of states. If so, what observable(s) can yield the charge carrier density? How can you measure these observables?

The question looks long, but the answer should be condensed into a basic principle...I hope.

Try looking into tunneling spectroscopy. One can measure the I vs. V (current vs. voltage) across the tunneling junction, or measure the second derivative dI/dV. This is equivalent to the tunneling conductance. What is interesting here is that the normalized conductance is equivalent or proportional to the density of states, depending on how complicated the tunneling matrix element is for that particular material and tunneling geometry.

Zz.

Thanks Zz.

Can you give me a reference where I can see exactly how the second derivative dI/dU relates to the density of states?

Thanks.

E.L. Wolf has a definitive text on tunneling spectroscopy in solids, that I used as a graduate student. That might be a good place to start.

Zz.

afrano,

one of the most straight forward ways of measuring the DOS is to use photo electron spectroscopy, which is found in most well equipped surface science labs. We have one our lab. the principle is based on the photoelectric effect and will give you only the LDOS (local density of states) of the atoms near the surface. Mind you, the information obtained isn't bulk information, but it may be sufficient for your purposes.

modey3

Modey3 said:
afrano,

one of the most straight forward ways of measuring the DOS is to use photo electron spectroscopy, which is found in most well equipped surface science labs. We have one our lab. the principle is based on the photoelectric effect and will give you only the LDOS (local density of states) of the atoms near the surface. Mind you, the information obtained isn't bulk information, but it may be sufficient for your purposes.

modey3

We need to be a bit careful here. Photoemission spectroscopy may not necessarily produce a DOS. ARPES, for example, doesn't give you the DOS. What it does give you is the spectral function at a particular momentum. To get the DOS, you have to average out over all momentum values, and this is assuming that the matrix element doesn't play a significant role in transition probability.

Furthermore, even after doing the averaging, it will only tell you the DOS of the occupied side of the band. It cannot probe the unoccupied side the way tunneling spectroscopy can.

Zz.

Last edited:
Zapper,

I was not suggesting going as far as looking at the distribution of occupancies in reciprocal space. I was merely suggesting using photoelectron spectroscopy to get the occupancy at a particular energy which means I don't have to use ARPES. Traditional photoelectron spectroscopy will not tell you anything about the band structure, but it will give you information about the occupied energy levels.

modey3

1. What is the density of states?

The density of states (DOS) is a physical quantity that describes the number of states per unit volume available to be occupied by particles in a given energy range. It is an important concept in solid state physics and is used to understand the electronic and thermal properties of materials.

2. Why is measuring the density of states important?

Measuring the density of states is crucial for understanding the behavior of materials, especially in electronic and optoelectronic devices. It can provide information about the energy levels available to electrons and how they are distributed, which can help in designing and optimizing materials for specific applications.

3. How can one experimentally measure the density of states?

One common experimental method for measuring the density of states is through spectroscopic techniques such as photoemission spectroscopy or tunneling spectroscopy. These techniques involve exciting electrons in a material and measuring the energy and intensity of the emitted electrons, which can then be used to calculate the density of states.

4. Are there any theoretical methods for calculating the density of states?

Yes, there are several theoretical models and equations that can be used to calculate the density of states. Some examples include the free electron model, the nearly free electron model, and the tight-binding model. These models use different assumptions and approximations to describe the behavior of electrons in a material and can provide useful insights into its properties.

5. Can the density of states be modified or controlled?

Yes, the density of states can be modified by changing the material's composition, structure, or external conditions such as temperature or pressure. For example, doping a semiconductor with impurities can create new energy levels and alter the density of states, which can be used to tune its electronic properties. This control over the density of states is essential for designing and optimizing materials for specific applications.

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