Questions tagged [electronic-band-theory]
Use this tag to ask about band-structure formation in solids, or about how electrons and holes behave inside them.
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DFT Local Density Approach. Please, help me to understand some formulas [closed]
First of all i'd like to apologize for my poor English.
In general im quite bad in physics, but it turned out that i have to carry out some band structure calculations. I've already done some with ...
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How are atomic orbitals ascribed to crystal bands?
It is possible to understand band formation by considering a free electron dispersion relation $E(\vec{k})=\frac{{\hbar}^2k^2}{2m}$ which is modified when a periodic potential $V(\vec{r})$ is ...
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How do you calculate the electric field from conduction and/or valence band energy?
I am currently using a program to calculate the band diagram of a semiconductor structure in 3D. I am wondering if its possible to use the finite difference method to calculate the electric field. ...
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40 views
How can electrons travel from the valence band into the conduction band?
I'm currently studying Introductory Semiconductor Device Physics by Parker.
In band-theory, we know that if an electron is at the top of an energy band, then there are no allowed states immediately ...
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24 views
How to prevent recombination of carriers?
Let say we have a contact of an electron conductor and a hole conductor. How is it possible to prevent recombination of the carriers nearly completely? So, electrons do not suppose to fly or tunnel ...
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40 views
Why do semiconductor lasers become weaker after extended use (not due to battery)?
Why do semiconductor lasers become less bright as they are used for longer periods of time (assuming their battery is full)? Does it have something to do with the PN junction reaching some kind of ...
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70 views
Are holes electrons moving in the same direction of the electric field?
Holes are electrons, but with negative mass. That's said, so by applying electric field, electrons(n) move in the opposite direction of the field, while holes(other electrons) move in the same ...
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1answer
35 views
Why does the energy levels in electron bands lay so closely together?
I'm currently trying to figure out how electron bands form in solids. The Pauli exclusion principle states that:
two or more identical fermions (particles with half-integer spin) cannot occupy the ...
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1answer
38 views
Where do photons excite electrons in the PN junction?
Assuming a Si-Boron P-type, and Si-Phosphorous N-type solar cell.
N-type is on top and P-type is bottom.
I understand that after both semiconductors are layered a depletion zone is formed. Where e- ...
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Why does nMOS using N+ gate have lower Vth than nMOS using P+ gate ? (w/o band diagram)
I understand it from band diagram.(Band bending is more stiff in N+ gate case)
However, I don't know what's essentially happening.
If P+ gate and N+ gate have same dose, their poly depetion will be ...
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0answers
38 views
Energy bands. Bonding and antibonding orbitals
In tight-binding wikipedia article it is said that bonding and anti-bonding orbitals correspond to different $k$-values in a single energy band. At the same time in Cordona Fundamentals of ...
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5answers
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Can we / should we use the Pauli principle to explain band structure?
Checking the wikipedia article on band structure, I got caught in major doubts...
They try to give an intuitive explanation of the band structure relying heavily on Pauli Exclusion Principle:
if a ...
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36 views
Electronic band structure of proteins
Proteins are a class of macromolecules. What range of electronic band structure do These have? Are These more like semiconductors? Or like insulators? How high is the typical Fermi Level for Proteins?
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Is there a simple rule connecting all indirect semiconductors band gaps to their electron-hole pair generation average energy?
The band gap of Diamond, Silicon and Germanium is 5.5, 1.12, 0.66 eV while the average energy to produce an electron-hole pair for
the same semiconductor is namely 13, 3.6 and 2.9 eV. This ratios are ...
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3answers
88 views
Electronic band structure
I want to know why the bands like valence or conduction splits up into two parts as shown in this diagram. why the energy gaps exist with in these bands? As you can see in this diagram that their is ...
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Why does first photonic band go to zero at the centre of the Brillouin zone?
I have been plotting photonic band diagrams of various geometries recently and I identify if it is correct by looking if it goes to zero at the Brillouin zone centre, $\Gamma$. I realised early on ...
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Putting high symmetry points labels to a band structure plot [closed]
So far I've got this plot using Quantum Espresso. I want to put gamma, X, L, etc labels to the k-path.
Quantum Espresso's ouput states the following:
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At what temperature is the band gap value when obtained from Arrhenius plot?
Using the equation
$$\ln{R}=\ln{R_0} + \frac{E_G}{2k_B T}$$
we can obtain the band gap value $E_G$ by measuring a sample's resistance $R$ with changing temperature $T$ and using the parameters of the ...
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45 views
What is the binding energy between conduction band and valence band of metals and insulators?
As far as my understanding of solid state physics goes, I can't see a clear connection between binding energy and band gap. But our teacher asked us the question as an assignment but i really can't ...
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1answer
86 views
What does the concept of “free electron” mean in the context of band theory?
Often when conductivity is explained through band theory, the term "free" tends to crop up. As an example, I often come across descriptions of the valence band as a highest filled set of states ...
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52 views
Energy band gap
I am studying from the Aschroft & Mermim. In the chapter 8 they prove the Bloch theorem and introduce the concept of band.
they say that k is a quantum number that charactrize the eigenfunction ...
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6answers
247 views
Can amorphous solids have energy bands?
One can understand the formation of energy bands from the Kronig-Penny model which assumes a periodic potential. But I heard that even if the potential is aperiodic, for example in amorphous ...
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1answer
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Is the band theory valid for an electron with energy greater than the potential?
Consider Kroenig Penney model. Here there is a derivation that uses the following potential:
One of the assumption is that the energy of the electron is $E<U_0$. Under this assumption (and others) ...
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1answer
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Why does the 2D hexagonal lattice have a different tight binding band structure than Graphene?
Here you can find band structures for various tight binding models. I was wondering, why the 2-D hexagonal lattice has a different band structure than Graphene, even though they have the same lattice.
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How to calculate conductivity / electron mobility from theory?
Is there a way to make quantitative statements about the conductivity of materials with band theory?
If not I should still be able to get information about the conductivity from Green-Kubo relations ...
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How can I calculate the chemical potential and the effective masses in an intrinsic semiconductor?
I want to calculate the chemical potential and the effective masses of the germanium charge carriers considering that the relaxation time is the same for the two carriers: electrons and holes. ...
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How can I draw the energy bands for the first and second zones of Brillouin? Is it conductor or insulator?
I want to draw the energy ($E$) diagrams for a simple cubic cell of parameter $a$, where each atom provides two electrons for the almost free electron levels for planes [100], [110] and [111].
I ...
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2answers
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Orbitals without overlaps in band structures of solids
We know every band in the band structure of solids is the result of overlaps of an orbital type. My question is that when there is not any overlap between a type of orbitals(which may be the lowerest ...
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1answer
51 views
Is diamond able to conduct electricity given 5.5 eV of energy? How do we then identify insulators and semiconductors?
I have learnt that the band gap for diamond, an insulator, is $5.5\:\rm eV$. Does this mean that diamond is able to conduct electricity if we give it this immense amount of energy (let's assume we do ...
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3answers
618 views
Conduction and Valence band
What is the difference between a conduction and valence band ? How an electron will behave different in conduction and valence bands ? When an electron leaves an atom the atom becomes ion. Does it ...
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1answer
61 views
Can someone give a simple mathematical explanation of the tight binding method?
I'm trying to understand the tight binding method but I'm struggling with a lot of the mathematical formalism. A lot of the mathematical formalism I read jumps into explaining it a few too many steps ...
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0answers
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What is it about metal elements that means their conduction and valence bands overlap, as opposed to non-metal elements where there is no overlap?
I can't see why metals have overlapping bands and a higher Fermi level compared to Non-metals where there is no overlap and the Fermi level is not in the conduction band.
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Mental contradiction: Valence electrons do not move at the non-zero wavevector?
I have a mental contradiction. Let's consider the following band structure with the Fermi energy somewhere inside the gap:
where $\Gamma$ point represents the zero value of the wavevector $|\vec{k}|$....
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2answers
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What is the significance of the time $\hbar/E_F$ where $E_F$ is the Fermi energy?
For free electrons in a metal, the Fermi energy $E_F$ (defined as the highest filled energy level at $T=0$). It represents a characteristic energy scale of the system as well as the energy of the ...
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0answers
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Rashba effect in 2DEG (how there is non zero electric field)
In the right column of page 20 in this paper, spins in few-electron quantum dots, the paper says "It is at first sight surprising that there
is a net spin-orbit interaction: since the state is bound
...
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The Hermicity of k.p Hamiltonian with operator ordering?
I am trying to use the k.p method to study quantum well band structure. One example Hamiltonian look like this [J. Appl. Phys., 116, 033709(2014)]
[]1
where
${{\hat k}_ \pm } = {{\hat k}_x} \pm i{{\...
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2answers
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Is Fermi Level a property of the material?
I have gotten myself confused about the band structure explanation of semi-conductors vs insulators. The Wikipedia picture
and the explanation surrounding it seem to suggest that Fermi Level is a ...
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1answer
180 views
Is topological surface state always tangential to bulk bands?
Think of a topologically nontrivial $D$-dimensional system. Its bulk bands form a $D+1$-dimensional manifold ($+1$ from energy). Its surface/edge bands form a $D$-dimensional one. Is the latter always ...
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1answer
156 views
What happens when we add free electrons to an insulator?
I'm trying to understand why an insulator doesn't conduct electricity. If I understand correctly, the energies of electrons of an insulator are bound tightly to the nucleus, so there are no free ...
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Variational calculus and KKR method for band structure calculation
I’ve been studying the KKR method from the original Kohn and Kostoker’s paper (https://journals.aps.org/pr/abstract/10.1103/PhysRev.94.1111).
On the text, they use variational calculus for dealing ...
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1answer
140 views
free electron approximation verses tight binding approximation
What is the relation between electronic band structure that is calculated by using free electron approximation (FEA) and tight binding approximation (TBA)?
My understanding:
In FEA, it seems we ...
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1answer
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Can the graphene's conductivity be explained using only orbitals?
I am trying to find a 'easier' or more 'intuitive' way to calculate the conductivity of graphene. I want do this by using atomic or molecular orbitals. Anyone have a clue about how this can be done? ...
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Fermi Dirac probability relative to electrons and holes
I'm having a hard time to understand the following sketch:
especially in case of the second diagramm. What does E against f(E) mean? How do I interpret this? The probability f(E) of an electron is ...
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1answer
64 views
band gap energy (discrete or continous?)
What does the band gap energy mean explicitly? Is it a single, discrete energy or is it a energy region? Sketches always show a "gap" between the conduction and the valence band so I assume there are ...
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1answer
111 views
Why is there a difference between Fermi levels in metals and metal-oxide semiconductors (MOS)?
Why are Fermi levels in metals lower than the Fermi level of $\text{p}$-substrates in metal-oxide semiconductors (MOS)? Specifically, why is there a difference of $qV$?
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2answers
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Energy of electrons?
Whats meant by energy of electrons in different orbits of atoms. Does this means that the electrons at higher evergy levels have more kinetic energy as compared to the electrons at lower energy level ...
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Why do we need to know “two-bands” Hall coefficient and magnetoresistance?
I know only partially filled bands result in current density, and I think there must be not only 2 partially filled bands, but "several" partially filled bands. For each partially filled band, its Ohm'...
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Acceptors with very high energy level in semiconductor
I have gallium arsenide (energy gap of 1.4 eV) doped with silicon in concentration of $10^{14} cm^{-3}$ and energy level very close to the conduction band so it's act like a donor. Now we put in also ...
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Band theory- Is the conducting band the last orbital with a gap between the two bands?
What I understand is in each atom there are conducting and valence bands
and the valence band, the minimum level for electrons (is the orbital before the last)
Is the conducting band the last ...
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142 views
Band structure and Density of states (DOS)
Can someone explain how these two plots are related?
How are the peaks in the right are associated with the left figure?
