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-2
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0answers
11 views

Bandlike vs. Excitonic Semiconductors

What is the different between 'bandlike' semiconductors and 'excitonic' semiconductors and how does this relate to whether they are organic or inorganic? I also wonder how such bandlike or excitonic ...
1
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1answer
14 views

What's the difference between semiconductor and insulator (besides band gap)?

The typical classification of electronic materials is metal-semiconductor-insulator. Is there any actual difference between a semiconductor and an insulator, besides the size of the bandgap?
0
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0answers
8 views

Can I use an IV curve alone to differentiate between metallic, semiconducting and insulating materials?

Assuming the size of the bandgap is expressed as resistance in the IV curve, could I tell between metals, semiconductors an insulators by only doing an IV sweep? For example very high slopes (large ...
1
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2answers
124 views

Can excitons be understood in terms of classical quantum physics?

From what I understand, an exciton is an electron-hole pair in a semiconductor that exists in a bound state (through the electrostatic potential). I have seen it stated that this pair behaves in a way ...
0
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0answers
7 views

Connection between fermi velocity and mean (square) velocity of diffusion current

Is there any connection between $v_{F}$ and the $<v^{2}_{diff}>$, lets say for electrons in metals? I have come to a conclusion, that they are the same order of magnitude and their equivalence ...
1
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1answer
103 views

Effective masses for different direction

Assume we have an indirect semiconductor where the effective mass becomes anisotropic in different directions. Usually, one talks about a mass in parallel and perpendicular direction referring to ...
9
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2answers
69 views

Why is there a band structure for strongly correlated systems?

The existence of band structure of a crystalline solid comes from the Bloch theorem, which relies on the independent-electron approximation. Why do people still talk about the band structure for a ...
1
vote
1answer
54 views

What is the physical meaning of an electronic system evolving adiabatically through a closed path?

I am trying to understand Physics behind the Weyl Fermion in Condensed Matter Systems. Electrons show Weyl fermionic behaviour in the vicinity of so called 'Diabolical Points' in the band structure. ...
0
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2answers
90 views

What can we learn from a band structure diagram?

Other than the band gap and its magnitude, what are the things that we can immediately learn about the properties of the material just by glancing at its band structure? Can we say something about ...
3
votes
1answer
130 views

Are there measurable quantities which directly depends on the Fermi velocity?

The dispersion relation of electrons in, for example, graphene exhibits Dirac cones. The dispersion relation of a Dirac point at $\mathbf{k}=\mathbf{K}$ is linear in the momentum magnitude: $$E=\pm ...
1
vote
1answer
789 views

What is the secondary electron cutoff in ultraviolet photoelectron spectroscopy?

While the fasted emitted electrons comes from the fermi level of the material in UPS measurement, where does the slowest, which is called secondary electron cut-off orginate from? I really can't ...
0
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0answers
491 views

How are band gap energy, dielectric constant (permittivity) and resistance related to each other?

The following three properties are related to current flow: Band gap energy Dielectric constant Resistance I would expect them all to have the same trend (i.e. higher band gap energy would cause ...
1
vote
1answer
24 views

How do phonons affect the work function?

How do phonons affect the work function? Could phonons that are directed towards a single atom, such as in a body-centered cubic crystal, increase the amount of thermal excitation and thus decrease ...
3
votes
1answer
186 views

Hartree-Fock correction to $e$-$e$ interaction

The corrections to the energy per electron in a jellium model (uniform distribution of positive ion charge approximation to the regulated long range order ionic array) is given by (in units of Ry) ...
0
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0answers
15 views

Do the band lines along high symmetry points contain all the information of the first Brillouin zone?

When calculating the electronic structure of solids, one usually plots the band structure along a certain set of paths that connect high symmetry points in the first Brillouin zone(IBZ). I wonder ...
4
votes
1answer
229 views

In a positively biased PN junction, where do the injection carriers come from?

I am not quite understand i-v character of PN-junction diode. Here is the model in textbook. The PN junction diode can be divided into three regions. They are One depletion region near the PN ...
9
votes
2answers
224 views

Why are band maxima / minima often (always?) at high-symmetry points?

(inspired by this question.) In every semiconductor that I can think of, the valence band maximum and conduction band minimum are at a high-symmetry point in the Brillouin Zone (BZ). Often the BZ ...
3
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0answers
51 views

What is the physics behind “Bulk-edge correspondence”?

There is a frequently mentioned concept in the field of topological insulator called "bulk-edge correspondence" or "bulk-boundary correspondence", which basically gives the relationship between the ...
1
vote
7answers
352 views

Quantization vs. continuous energy levels

I still don't get what it means for atomic energy levels to be continuous or quantitized (incontinuous). Clearing this up will really help me. Also, can anyone tell me why energy levels in solids are ...
0
votes
2answers
49 views

Conduction bands and Valence Bands, so do electrons really exist in Conduction bands?

My understanding is that conduction bands are energy bands created from the electrons in the valence shells/bands absorbing energy to jump to the next level (is this true)? Now, do the conduction ...
1
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0answers
26 views

DOS behavior of Van Hove singularity in a line

When there are some points in momentum space give $|\nabla_k \varepsilon_k|=0$, they are called Van Hove points and give singularity in the desity of states (DOS). But what if $|\nabla_k ...
0
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0answers
23 views

How to get DOS of Van Hove singularity using quadratic dispersion relation

Take 2D case for example. We can first get the area in momentum space for all $k$ that satisfy $E_0<E(k)<E $, say $S(E)$. And the density of state (DOS) is $\rho(E)=\frac{\partial S(E)}{\partial ...
1
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0answers
47 views

DOS of Van Hove singularity in 2D square lattice tight binding model

For the simplest example, 2D square lattice tight binding model gives the energy band as $$\varepsilon_k=-2t(\cos k_x+\cos k_y) \, .$$ We know that $\vec{k}=(0,\pi)$ and related momentum points are ...
2
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0answers
46 views

DOS integral when surface is not closed

According to the density of states (DOS) formula $$\rho(\varepsilon)\propto \int_{\varepsilon=\text{const}}\frac{dS}{|\nabla_k \varepsilon_k|}$$ Since there is an integral on the constant energy ...
0
votes
0answers
31 views

How to get the asymptotic expression of DOS near Van Hove singularity [duplicate]

For the simplest example, 2D square lattice tight binding model gives the energy band as $$\varepsilon_k=-2t(\cos k_x+\cos k_y) \, .$$ We know that $\vec{k}=(0,\pi)$ and related momentum points are ...
1
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0answers
30 views

kp theory of QW band structures in envelope function approximation

I am currently trying to calculate wave functions and energy dispersions for quantum well heterostructures. The kp method is my choice to do that. I already calculated band structures for bulk ...
3
votes
3answers
301 views

What does $m^*>m_e$ imply? (the effective mass of electron is larger than its rest mass)

From what I understand, the concept of effective mass is just something people come up with to make electrons and holes obey the equation of motion $$ \vec{F}=m^* \vec{a} $$ without dealing with the ...
0
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0answers
39 views

Relation between energy band gap and atomic number

Is there any relation between energy band gap in group4 elements and their atomic numbers? It might be just a trivial observation but I noticed How from Carbon to Germanium the band gap went from ...
0
votes
0answers
11 views

Silicon interface trap filling in nonequilibrium conditions

I need to know probability of filling of interface traps with energy levels located in silicon bandgap. In equilibrium conditions I can use Fermi level and Fermi–Dirac statistics to calculate ...
0
votes
1answer
18 views

Are there electrons in the electron energy levels that are created due to doping in N type semiconductors?

I was going through this article.There it is mention that The addition of donor impurities contributes electron energy levels high in the semiconductor band gap so that electrons can be easily ...
0
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0answers
36 views

Klein paradox in graphene

When considering the Klein paradox in graphene Katsnelson, Novoselov and Geim introduce a potential barrier (see http://www.nature.com/nphys/journal/v2/n9/full/nphys384.html). But I cannot understand ...
0
votes
0answers
18 views

Why are reciprocal lattice vector periodic, and time-frequency not?

k-space vectors are related to each other by $k=k'+G$, where $G$ is the reciprocal lattice vector $G=2\pi/a$. This means that the frequency of oscillation in real space of a plane wave $e^{ikx}$ is ...
2
votes
1answer
105 views

Is Chern-number for free fermion system always limited by total band number, i.e. number of orbits with a unit cell?

If so, how to see that? Also I think it has been proven that the total Chern-number for free fermion system is 0? If you know how to prove it, please make some comment or hopefully a sketch of ...
1
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2answers
342 views

DFT for bandstructure

Density Functional Theory (DFT) is not appropriate in predicting the band gap of the materials. However, which functional gives close value to the experimentally observed band gap of semiconductors? ...
1
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1answer
194 views

band structure of Topological insulators

The above figure is Rashba-split free electron-like surface state in a projected bulk band gap. The bellow figure is the band structure of Topological insulators. x axis is the wave vector, y axis ...
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0answers
27 views

Why graphene's substrate is important

I just have some feelings that somehow it is important what specific subtrate is used to grow graphene monolayer on. Some substrates are better, another ones are not so good. But I cannot completely ...
5
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1answer
174 views

Understanding electronic band structure diagrams

Currently I'm trying to understand electronic band structures such as depicted below: And following questions were arisen. Why are there multiple lines in valence side and conduction side? Where ...
2
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2answers
5k views

Effective Mass and Fermi Velocity of Electrons in Graphene:

In graphene, we have (in the low energy limit) the linear energy-momentum dispersion relation: $E=\hbar v_{\rm{F}}|k|$. This expression arises from a tight-binding model, in fact $E =\frac{3\hbar ...
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0answers
53 views

Problem with energy bands

I am getting confused by the energy bands. As far as I know, the outermost shell of an atom is called valence shell. The electrons residing in that shell participate in reactions and conduction of ...
1
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2answers
57 views

Does exciting an electron across the band gap change either its position or its localization?

I suspect that exciting an electron from its valence band to conduction band doesn't change its position, since the difference between the two bands are just their energies, but I want to know for ...
1
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1answer
1k views

What is the reason behind band gap narrowing in semiconductors

I want to know why some semiconductors band gap decreases after doping with elements. Burstein-Moss band-filling effect can be useful to explain band gap widing in a semiconductor materials but i was ...
2
votes
2answers
40 views

Shining light (of a particular frequency) on an insulator to make it into a conductor

Recently I read about band theory of solids. The energy difference between valence band and conduction band determines the conductive property of solids. Suppose I take an insulator and shine it with ...
1
vote
2answers
139 views

Why does the “counting rule” of band theory fail to predict the conduction properties of some materials?

I'm a little confused by the description I commonly hear about the electron counting rule in band theory. The general statement I find is that a "solid with an odd number of electrons per unit cell ...
0
votes
0answers
24 views

Strain effects on conduction band edge in k.p theory

While including strain effects into the k.p theory, I often see that the heavy- and light-hole band edges are modified due to the strain, but not the split-off or conduction band edges (e.g. this ...
0
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1answer
331 views

How to obtain band dispersion from a band structure diagram?

Reading about bands dispersion, I came across the following (Computational Chemsitry of Solid State Materials): ...
2
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1answer
42 views

Why does band gap form for Silicon?

The image on the right shows that as the interatomic distance becomes closer together, the 3P and 3S band that joined together begins to split up forming a gap in allowed energies. Why does this ...
0
votes
1answer
3k views

How does temperature affect a semiconductor band gap?

From this link, I've read that An increased interatomic spacing decreases the potential seen by the electrons in the material, which in turn reduces the size of the energy bandgap. Can this ...
2
votes
1answer
79 views

How to check the ohmic contact to the film?

I have a thin semiconductor film deposited on an isolating substrate. I would like to check different metals to find out do they form the ohmic contact or Schottky barrier. What is the best way to do ...
3
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3answers
106 views

Do electrons in the conduction band have a quantum number?

Sorry if this is a silly question, but I haven't seen the concept anywhere and was wondering why. If valence electrons can have a quantum number, why can't conduction electrons? Is there something ...
0
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1answer
153 views

Factors on which barrier potential in a p n junction depends

I have a few queries regarding the barrier potential in a p-n junction diode. Is the barrier potential dependent on temperature? Why/why not? Does the barrier potential depend on doping ...