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3answers
123 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 ...
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2answers
57 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 ...
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2answers
56 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 ...
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1answer
177 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 ...
3
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1answer
124 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) ...
2
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1answer
19 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 ...
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1answer
32 views

What do we get from the diagonalization of the $k\cdot p$ matrix?

In k.p theory, we expand the wave function around a known point ${\bf k}_0$ $$u_{\lambda}({\bf k})=\sum_{\nu} c_{\lambda,\nu}({\bf k})u_{\nu}({\bf k}_0).$$ If we now consider 8 bands (conduction, ...
1
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1answer
71 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 ...
1
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1answer
595 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 ...
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1answer
21 views

Why an undoped heterojunction causes potential barrier?

In this image (source) a potential double-barrier was created using GaAs and AlAs lattices (undoped). Why would any potential barrier be formed, if all the bonds are electrostatically balanced (i.e. ...
0
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1answer
79 views

Metals/Insulators and Electron Counting

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 ...
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0answers
831 views

Where does the Berry phase of $\pi$ come from in a topological insulator?

The Berry connection and the Berry phase should be related. Now for a topological insulator (TI) (or to be more precise, for a quantum spin hall state, but I think the Chern parities are calculated in ...
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0answers
217 views

Derivation of existence of energy band gap in semiconductor (solid State)

I am looking for both a mathematical and a physical reason for energy band gap in metals. For Physical reason, I was told that at each reciprocal lattice, you could have Bragg scattering, that would ...
2
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0answers
128 views

Why does silicon have an indirect gap?

Is there an intuitive explanation as to why silicon has an indirect gap? I have heard that this can explained using pseudopotentials.
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0answers
159 views

Problems while numerically computing band structure using k.p theory

I want to use k.p theory to numerically compute the band structure of a bulk semiconductor. The band I like to include are the lowest conduction band (cb), the heavy-hole (hh), the light-hole (lh) and ...
1
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0answers
90 views

Why the current through a resonant tunnel diode drops when the bound state goes below the conduction band?

The IV curve of a resonant tunneling diode is N-shaped. The rise in current flow happens because the bound state (the energy state in the well) enters the thermal area of the conductor ($\mu_1 + ...
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0answers
38 views

Symmetry breaking and band gaps?

Can the discontinuity in the E-K dispersion relation of a periodic lattice (at the boundary of a Brillouin zone) be understood as a consequence of breaking continuous translation symmetry into ...
1
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0answers
43 views

How come graphene is considered to have two valleys?

The typical graphene band-structure is a double-cone (in opposite directions to each other) with Dirac point in the middle. I assume the bottom cone is like the valence band, while the top cone is ...
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0answers
32 views

How can we determine the inbuilt barrierpotential and electric feld for a given band diagram?

Suppose I have got two p type silicon materials of different concentrations (the difference in thier concentrations is small but considerable enough that their fermi levels differ by noticeable ...
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0answers
21 views

Is there a way to quantify how similar a polycrystal should behave to a single crystal?

So in solid state classes we learned about phenomena like band structure and others arising from a periodic potential. Then we get to doing actual experiment and find out that materials being single ...
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0answers
10 views

Hydrostatically compressed crystal

When a crystal is hydro-statically compressed, the band gap becomes larger, however I am unsure why. Can anyone explain why to me in detail though?
1
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0answers
831 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 ...
1
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0answers
80 views

Nature of electron states in a semiconductor

Usually one is led to think of an electron moving from the valence band to the conduction band as an electron leaving the atom it is bound to in the lattice, and becoming free to move, while leaving ...
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0answers
158 views

Energy band diagram of a metal-silicon-metal device, bias voltage applied

I have an intrinsic silicon layer sandwiched in between two aluminum contacts. I'm trying to figure out the band diagram of the entire device when a positive bias (much larger than the work function ...
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0answers
306 views

Some questions about the edge states for time-reversal invariant topological superconductors?

Stimulated by my some recent calculations on edge states(ES) for time-reversal invariant(TRI) topological superconductors(TS) as well as many questions concerning the "edge states" in Physics ...
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0answers
11 views

What is the effect of doping silicon with an excessive amount of group V donors?

What is actually the effect of doping silicon with an excessive amount of group V / donor atoms? I read it reduces the conductivity but I dont understand why.
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0answers
32 views

What is a simple example of band structure having varying “orbital character”?

I'm trying to understand exactly what orbital character is in the band structure of a solid, such as that described in this paper and many others. I'm having trouble finding references online that ...
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0answers
35 views

electron-electron interactions in 1-D electron gas

The electron-electron interaction contribution to the hamiltonian in $k$-space representation is given by ...
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0answers
26 views

What's the elementary reason for the formation of a band gap?

Bohr's solution for an isolated hydrogen atom showed that there are only discrete allowed energy levels, $E_n = -{E_0\over n^2}$ and the solution of the Schreodinger equation provided a certain ...
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0answers
165 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 ...
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0answers
23 views

Couting the occupied states in band structure

I work with several dft codes and I have produced the band structures of some doped semiconductors with their plots. The problem I have is that I do not know how I can analyze the band structure and ...
0
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0answers
26 views

Quantum Forbidden Regions-Band Theory

In systems where certain regions are classically forbidden for a particle, quantum mechanics permits a finite probability of finding the particle in those regions. However, in band theory of metals, ...
0
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0answers
26 views

Computing Parity by numerical tables of characters

I have a table of the characters of a set of wavefunctions for different points in reciprocal space and for different band indices (this is for a solid). For the case of a single irreducible ...