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14 views

what is the effect of temperature on the resistance of a photoconductor?

As we know, for a photo conductor resistance tends to decrease with increase in irradiance, but with greater irradiance comes greater temperature. Also we know, photo conductors are ...
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1answer
29 views

Where can I learn about band theory?

I'm studying quantum mechanics and I want to understand perfectly where the bands of the electronic sturcture come from. I've read that it is related with the periodic potential, Bloch waves and ...
3
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1answer
33 views

Momentum operator in effective mass approximation

When we calculate the band structure of some solid then we often find that in the bottom of the conduction band the dispersion looks approximately quadratic with some new effective mass: $$E(k) = ...
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0answers
11 views

Effect symmetry on points in momentum space

I have to study some material for a condensed matter physics course and cam across a passage that I don't understand. "In momentum space time reversal symmetry and particle hole symmetry only have ...
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0answers
11 views

effect of inversion symmetry on the bandstructure

I have a very general question, but I hope that someone can answer it. Can someone describe what the effect of inversion symmetry is on the bandstructure. (Or is there not a general effect?). ...
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1answer
86 views

Energies in Band Alignments

There is something that I would like to confirm regarding the energy when aligning the bands of heterostructures. There seems to be a general consensus that there is no simple rule to align two ...
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0answers
11 views

How does electrical current affect electronic band density?

When sending a current through a conductor, electrons in the valence band gain energy. What does that mean concretely? Are electrons excited uniformly, i.e. all electrons in the valence band gain ...
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0answers
10 views

Why singlet and triplet states are not mentioned when dealing with inorganic semiconductors or other heavy materials?

Singlet and triplet states get attention in organic materials (fluorescence, phosphorescence, upconversion). Why singlet/triplet states are never mentioned in the context of inorganic semiconductors, ...
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0answers
7 views

Electronic Transport not covered by Bandstructure in Solid State Physics

From what I have read, most of the electronic transport phenomena in solids state physics seems to able to be determined with the bandstructure. Schottky Barriers, bandgaps, band discontinuities can ...
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0answers
20 views

Are Dirac points the norm for 2D band structure?

I've been doing simulations of band structure for 2D optical lattices, and something I've noticed is that, for sufficiently shallow lattices, there are typically points on the edge of the first ...
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0answers
32 views

Tight-binding model parameters fitting from ab-initio calculation results

Or the problem can be rephrased as: How to extract the tight-binding parameters from first principle calculations? I have searched some articles but all of them just give vague descriptions when ...
1
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1answer
37 views

Can the electron go below ground state due to the Zeeman effect?

I've read that the Zeeman effect can cause a single allowed energy level to split into two, one of which is higher in energy by some value \Delta E'. The other level is shifted down by the same ...
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0answers
23 views

Could Hamiltonian near band touching point be non-linear?

We all know the Hamiltonian of weyl semimetal is +/- $\vec k\cdot \vec \sigma$, thus give the +/- 1 total flux of each weyl point. And in the band structure of real materials, if the perturbation ...
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0answers
19 views

Obtaining a Positive Hall Coefficient for Electrons Near the Top of a Valence Band

Using a Drude model of charge carriers with a charge $q$ and a mass $m$ (which I allow to take either sign at this stage) in a sample with an applied electric field $\mathbf{E}$ and magnetic field ...
1
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1answer
36 views

What is invalidated when turning on many body interactions in a crystal?

I have just started to think about strongly interacting particles and Fermi liquid theory, and I have two questions. For non interacting particles moving in an potential field, we know that the ...
3
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2answers
70 views

Nearly Free Electron Model and the Reduced Zone Scheme

When for example studying the vibrational modes of a one dimensional diatomic chain we find that the dispersion relation $\omega(k)$ is periodic in the one dimensional reciprocal lattice vector ...
0
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1answer
34 views

electron blocking layer and hole blocking layer

What is basically an electron blocking layer and a hole blocking layer in contrast to an electron transport layer or a hole transport layer? In terms of the bandgap, I think if the case is one of a ...
1
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0answers
27 views

Single particle approximation for a conduction band electron?

I have a problem which on some levels appears very simple, but others quite complex so I thought I'd ask here to make sure I am on the right track before going ahead any further I have a 3D potential ...
0
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1answer
41 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
29 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
86 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 ${p_x}{p_y}{p_z}$ ...
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2answers
396 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 ...
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1answer
49 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
73 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 ...
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1answer
120 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 ...
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1answer
61 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
34 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 ...
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1answer
203 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 ...
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2answers
52 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 ...
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1answer
54 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
149 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
46 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
47 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 ...
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2answers
175 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.
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0answers
47 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
24 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
54 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 ...
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1answer
133 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
106 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?
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0answers
31 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
22 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
44 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
19 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
48 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
54 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 ...
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0answers
80 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
41 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
76 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
85 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 ...
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1answer
125 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 ...