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1answer
27 views

Basic question about valence/conduction bands

In most introductions to solid state physics that I've read, they explain the origin, basically, of the band gap as follows: By doing a superposition of the standing waves inside a BZ, one can find ...
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0answers
18 views

Help finding peak electron concentration? [on hold]

Any tips or thoughts on how to do this problem? Thank you!
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0answers
25 views

Why for each electron – hole recombination, an electron from the negative terminal of the battery is released

Why for each electron – hole recombination, an electron from the negative terminal of the battery enters the N-region and then drifts towards the junction?
2
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1answer
77 views

Does momentum space have a speed limit?

In ordinary $xyz$ space, the maximum velocity of propagation for mass-energy and/or information is $c$. So, my question: Is there also a maximum velocity of propagation in momentum ${p_x}{p_y}{p_z}$ ...
5
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2answers
207 views

Why is diamond transparent while graphite is not?

Diamond and graphite are both made of the same atom, carbon. Diamond has a tetrahedron structure while graphite has a flat hexagonal structure. Why is diamond transparent while graphite is not (at ...
0
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1answer
26 views

Magnitude of the band gap

In Kittels book on solid state physics (Introduction to solid state physics, p. 167, 8th ed.), he defines the band gap energy $E_g$ as $E_g = \int_0^1 U(x) [|\psi (+)|^2 - |\psi (-)|^2]$ where ...
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0answers
41 views

Band gap origin

Many introductory books on solid state physics use images that I find confusing. For instance, one picture I see alot when reading about the band gap, is similar to this one: I understand that the ...
1
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1answer
37 views

Why do we have heavy and light hole bands in semiconductors?

On the topic of the valence band of a semiconductor (in this example GaAS), it is the case that the valence band has some structure to it. As shown in the illustration below, we see that at the ...
1
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1answer
41 views

Relation between energy bands and Brillouin zones

In almost every book about solid state theory, electrons in a periodic potential are introduced and calculations for the dispersion relation $E(k)$ are presented. One obtains the usual pictures in ...
0
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1answer
27 views

What does it mean that an electron-hole pair is the fundamental unit of generation?

I wasn't certain to post this in chemistry or physics section. I was reading the wikipedia article on "Carrier generation and recombination" and in the second paragraph it says something that I ...
0
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1answer
185 views

Can a perfect insulator, i.e. matter devoid of all electrons conduct electricity?

Few weeks ago an article on Nautilus was published on Neutron stars. After reading that, a question was asked by a friend of mine. He asked if matter in neutron star would be able to transfer ...
0
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2answers
43 views

Translating Electronic Bands back to first Brilluoin Zone

For phonons, I understand why we can translate everything back into the first Brillouin Zone: there is a minimum wavelength defined by two lattice sites. For electrons, which are delocalized, I see ...
0
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1answer
52 views

What are the current carriers in a PN junction?

Imagine a PN junction in forward bias mode. The conventional current goes from the p-side to the n-side. However, as mobile holes move to the n-side, aren't there mobile electrons on the n-side which ...
4
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2answers
141 views

For the transition metals, how does counting the number of up-spins and down-spins still give you a non-integer magnetic moment?

The transition metals like Fe, Co and Ni have magnetic moments of 2.2, 1.7 and 0.6 Bohr magnetons, respectively. The band theory says that you get this when you calculate the density-of-states of the ...
2
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1answer
31 views

Metallic and Semiconducting Nanotubes, symmetry discussion

I'm interested in band gaps of Single-walled Carbon Nanotubes (SWNTs). I know that there are three kinds of SWNTs: Zigzag : $(n,0)$ Armchair : $(n,n)$ Chiral : $(n,m)$ Electical properties of ...
1
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1answer
40 views

Bandgaps of Silicon and their application in active optical elements

I know that silion has an indirect bandgap at $E = 1.12 \, eV $ or $ \lambda = 1.107 \, \mu m$ and I have read that active optical processes like absorption and emission have a decreased likelihood to ...
1
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2answers
154 views

Why do metals become insulators when oxidized?

I don't know the connection between how forming a new bond with oxygen then changes the density of states to transform the metal into an insulator. It seems like a very powerful transformation.
2
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0answers
33 views

Estimating Energy Bands For Dirac Comb Potential

With $$V = \sum_n aV_0(x-na) $$ I can solve exactly up to $$\cos(k a) = \cos(\kappa a) + \frac{2ma^2V_0}{\hbar^2}\frac{\sin(\kappa a)}{\kappa a} = f(\kappa a)$$ Where $E = \frac{\hbar^2 ...
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0answers
19 views

Choosing a basis state for density functional theory calculations

How do we choose basis set of wave functions for expanding the eigenfunctions of the kohn-sham equations? I mean given a material,what should i look for in order to choose my basis functions?
2
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1answer
38 views

Doped semiconductor: “what if all donated electrons are gone?”

I have trouble understanding conductivity of a n-doped semiconductor in the band theory. I know that donator atoms carry one excess electron that can enter the conduction band easily. If this ...
1
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1answer
64 views

Relation between band structure, dispersion, density of states, and the Fermi energy and Fermi level

Despite the long title, this question is mostly qualitative (although I am interested in quantitative results if possible). Say you have an electronic band structure (energy as a function of "k") for ...
0
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2answers
82 views

Density Functional Theory (DFT) calculation for metals

Why is DFT not used in calculating electronic structures and properties of metals? I know DFT calculations are not accurate for metallic structures. Can someone explain why?
1
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0answers
26 views

Spin flip scattering & Spin dependent scattering [closed]

What causes, i mean the mechanism spin flip scattering & spin independent scattering?
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0answers
18 views

Band structure and k vectors

If there is a restriction on the allowed states (k vectors) for a system, ie the no of states is equal to twice the number of unit cells in the crystal.. why do we plot k continuously on the x axis? ...
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0answers
28 views

element effect on quantum dot band gap

Main Question: Why do Au QDs have quantum confinement effects which change optical behavior from the bulk Au, whie certain other elements (such as Fe) are typically not shown to have the same ...
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0answers
17 views

Optically access a single valley in indirect semicondutors

An indirect semicondutor has an energetic minimum of its band structure at a point different from the $\Gamma$ point. But, there are multiple of them. Silicon for example has its band minimum at the ...
0
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1answer
30 views

Why dopant energy levels differ from one material to another?

Dopant levels in Si, Ge and GaAs are very different from each other. Even "similar" materials such as Si and Ge exhibit different dopant energy levels. (source: Pierret, Advanced Semiconductor ...
0
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1answer
46 views

How can a material be conductive and transparent at the same time?

Transparent conducting films for example. On one hand, the band structure of transparent materials must have a large enough HOMO-LUMO separation. On the other hand, conducting (metallic) materials ...
2
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0answers
57 views

Materials for use in a solar cell

In a solar cell, photons of the incident sunlight supply energy for excitation of electrons - a process which generates electron-hole pairs which can move under the influence of the electric field of ...
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0answers
35 views

Band-gap for solids with isoelectronic atoms

Isoelecronic atoms have same number of electrons but different nuclear charge. It is said that many of the chemical properties of these elements are equal or at least similar. Can I form solids with ...
3
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0answers
56 views

What is the effective electron mass in a plasma?

Is there a way to calculate the effective electron mass in plasmas? Effective electron mass is usually defined as varying from the vacuum electron mass in solid state physics. However, momentum ...
2
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2answers
79 views

Do metals *really* conduct at zero temperature?

The questions is mostly in the title, but might expose another of my misunderstanding of the band structure of solids and how that leads to metals and insulators. If we have a solid, and the fermi ...
1
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1answer
97 views

Density of States in NOT Free Electron Gas

I think that I understand how the density of states works for a free electron gas. It is effectively just a conversion factor between summing over values of k and integrating over values of E. If you ...
0
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0answers
27 views

determination of electron dispersion curves

I am somewhat new to quantum physics and I am studying electron dispersion band structures of SiC like the one here I want to know what spectroscopic techniques/methods or if they are spectroscopic ...
0
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2answers
79 views

Density Functional Theory (DFT) tutorial guide

I am going to start learning about DFT calculations. Could anyone advise me the best starting point for that? Simple example guiding tutorial with explanations would be great. Any input would be ...
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0answers
31 views

What is the “point” of STM?

Scanning tunneling microscopy (STM) measures density of states (DOS) in a sample. But angle-resolved photoemission spectroscopy (ARPES) measures the bandstructure $E(\mathbf{k})$ in a sample, from ...
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0answers
18 views

What is the meaning of band structure in the case of amorphous materials?

A consistent band structure is expected in crystals, because "everything is uniform". Theoretical calculations of band structure are also based on infinite lattice. In amorphous materials, however, ...
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0answers
22 views

How to determine the Fermi energy in Schottky barrier FET(SB-FET) channel?

The structure of Schottky Barrier FET(SB-FET) is almost the same with MOSFET. The difference between SBFET and MOSFET is the contacts change from Ohmic contacts to Schottky contacts. I know the way ...
2
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1answer
71 views

how do electrons in 2 separate atoms change its energy level when atoms come close together to form molecule?

The question is just as the title. It's said that electron must receive a specific amount of energy in order to go or drop to another energy level. So how can electrons of separate atoms which have ...
2
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1answer
44 views

at $T \approx 0 \, \text{K}$, will all energy levels within the electronic band structure be occupied up to a certain level?

I saw this from the script of my teacher that I don't understand what does it mean If we cool down a crystal to an absolute temperature of T ≈ 0K, all atoms of the crystal will exist at their ...
0
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0answers
45 views

Analysis of a Fermi surface

The following image shows the Fermi surface of Pb, plotted with XCrySDen. I have some difficulties in uderstanding the characteristics of that Fermi surface, in particular how to distinguish the ...
0
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0answers
39 views

what can be the BG and dielectric constant of monolayer MoS2 in semiconducting state (2H) and in metallic state (1T)

Monolayer MoS2 is a semiconductor that can undergo an MIT (Metal to insulator) or semiconducting state to insulating state transition. The semiconducting state is referred as 2H State and the metallic ...
0
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0answers
81 views

Band Structure from Fourier Transform Solution of Dirac Comb

I have use Fourier transforms to solve the Schrödinger equation for an attractive Dirac-$\delta$ comb potential of the form $$ V(x) = -\alpha \sum_{j = -\frac{N}{2}}^{\frac{N}{2}} \delta \left( x - ...
0
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1answer
26 views

Silicon parabolic dispersion for X minima

I am constructing a minimal model of the silicon conduction band minima for a monte-carlo program. Assuming the six equivalent bands are parabolic and spherical, since the conduction band minima lie ...
0
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0answers
20 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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1answer
42 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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1answer
102 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 ...
11
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3answers
119 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
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1answer
87 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. ...
1
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1answer
33 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 ...