Questions tagged [semiconductor-physics]

Semiconductor physics is the branch of solid state physics that focuses on specific properties of semiconductors. It studies dynamics of different perturbations (mainly electrons and holes) in the semiconductor crystal and the ways to harness it in electrical circuits.

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Understanding the Fermi level and the Fermi-Dirac distribution [duplicate]

I'm confused about why the Fermi level is located inside the band gap in semiconductors because it's defined to be the energy level where an electron has a 50% chance to be, but there can't be ...
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What are "electron holes" in semiconductors?

I'm tutoring senior high school students. So far I've explained them the concepts of atomic structure (Bohr's model & Quantum mechanical model) very clearly. Now the next topic to be taught is ...
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Why doesn't current flow in reverse biased diode?

Consider this reverse biased diode : I read that no or very small current flows in reverse biased diode as depletion layers get widened and huge resistance is offered so no electrons can cross it. ...
Ayush Pateria's user avatar
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Pn junction voltage drop?

This image from wikipedia, explains that there occurs a potential drop across a pn semiconductor junction, and an electric field confined to the depletion region. I already know the reason for the ...
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What determines the forward voltage drop for a diode?

I have always had the idea that the forward voltage drop in a semiconductor diode was related in a simple way to the bandgap energies in the semiconductor. However this is apparently not the case: ...
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Band gaps: are they at the centre or at the edge of the Brillouin zone?

Reading about electronic band structures, I came across the following: Band gaps open at the edges of the Brillouin zone (BZ), since that is where the Bragg scattering occurs. I am slightly ...
hat's user avatar
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What does Fermi level in the band gap mean?

What does it mean that the Fermi level for some semiconductors lie in the band gap? Is Fermi level definition different from what is know as usual? We define the Fermi level as the highest level of ...
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Why isn't there a potential difference across a disconnected diode?

I know this question sounds silly, as if there was a potential difference a current would be created when the terminals are connected together and this would mean energy has come from somewhere. The ...
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Why do $p$-orbitals correspond to the valence band in semiconductors?

Silicon is industry's most famous semiconductor. Its electron configuration is the following: It means that the highest energy orbitals are the 3p orbitals (which are only partially filled). Now, ...
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What is it about the "conduction band" of a material that is distinct from the valence band?

I'm taking a course in nanotech and we're discussing nanoelectronics. This has led to a discussion of conductors, semiconductors, and insulators. I have a number of lovely diagrams explaining the fact ...
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What is the concept of hole in semiconductor physics?

What is a hole? And how should we describe it to study it properly? Many textbooks refer to it as an empty state that carries a positive charge, but how can an empty state carry a positive charge? And ...
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The concept of Fermi level

I have read and used the concept of Fermi level previously and this is simply an attempt on my side to better my understanding of it by asking myself various questions. I understand that the fermi ...
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Reverse bias P-N junction [duplicate]

I am not able to understand why the PN junction does not conduct when reverse biased. Can't electrons travel from the N side through the power supply to the P side where they can jump from one hole to ...
user46169's user avatar
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What does the Fermi Energy really signify in a Semiconductor?

In understanding the behavior of semiconductors, I'm coming across a description of the Fermi Energy here and at Wikipedia's page (Fermi Energy, Fermi Level). If I understand correctly, the Fermi ...
Perrako's user avatar
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Why absence of electron is called hole?

I am having hard time in understanding the concept of holes: If there is no electron than how can it be a hole? For a moment lets assume absence of electron is termed as hole but how can this absent ...
johndaniel's user avatar
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How do electron holes have spin, and how do they interact with "real" particles / vice versa?

So, I thought I had an uneasy truce with quantum mechanics but I read something today which made spotted combat flare up in my mind again. In solid state semiconductor free electrons certainly have ...
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What are the phenomena responsible for irreversible increase in entropy?

https://www.quantamagazine.org/20140416-times-arrow-traced-to-quantum-source This article says that entanglement drives the arrow of time of increasing entropy towards thermodynamic equilibrium: ...
ScienceJournalist01's user avatar
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Are electrons in a p n junction delocalized across the junction?

When discussing p n junctions, it is usually said that electrons diffuse from the n side to the p side, hence creating a separation of charges. However, we know that electrons in a lattice are ...
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Effect of doping on the width of depletion layer of PN-junction diode

I've read that if there is very low doping in a pn-junction diode, the depletion region will be large because a large volume of depleted semiconductor is needed to generate enough electric field to ...
Sanatan Panigrahi's user avatar
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Electrical conduction using band theory

The often told cause of conductor conducting electricity is their valence band and conduction band overlap and when an electric field is applied the electrons jumps into conduction band and ...
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Difference between steady state and equilibrium?

In semiconductor physics, what is the difference between steady state and equilibrium. How analysis of devices varies in these processes?
johndaniel's user avatar
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Physical significance of electrons with negative effective mass. Are they holes or what?

For metals, the conduction band is less than fully filled, the effective mass $m^*=\hbar^2\Big(\frac{d^2E}{dk^2}\Big)^{-1}$ is positive for the interval $k\in[-\frac{\pi}{2a},+\frac{\pi}{2a}]$ of ...
Solidification's user avatar
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Electron holes in metals

For semiconductors, conductivity is given by $$\sigma=n|e|\mu_e+p|e|\mu_h$$ where $\sigma$ is conductivity, $n$ is the concentration of electrons, $e$ is the elementary charge, $p$ is the ...
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Why can solar cells be made of indirect and direct semiconductors? (Comparison between some pn-junction devices)

Various textbooks mention, but not go into detail, how semiconductor devices are optimized for their particular function. E-k space is trascendental to understand this, given that it depends on the ...
nomadStack's user avatar
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Temperature dependence of the relaxation time in Boltzmann equation for impurity scattering in metals

Is there any temperature dependence of relaxation time in impurity scattering of conducting electrons? It seems to me that there is none. But, some people claim that there is. So if you could explain,...
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How does current flow from the emitter, through the base and to the collector in a NPN transistor?

So, I understand that for a NPN transistor to work the emitter-base junction needs to be forward biased and the collector-base junction needs to be reverse biased. I understand how current flows from ...
tagonist's user avatar
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In the diode equation, why the exponential $\exp$ and the ideality factor $n$ are there? What do they represent & what is their significance?

In the Shockley diode equation, why the exponential $\exp$ and the ideality factor $n$ are there? What do they represent & what is their significance? I have to work on Solar Photovoltaics, and ...
Supreeth Kumar's user avatar
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Filled Band cannot generate current

In solid-state physics at $T=0 K$ considering the semi-classical approximation for electrons, I understand physically that if a band is completely filled, the electrons can't move and there is no ...
user239504's user avatar
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Are holes electrons moving in the same direction of the electric field? [closed]

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 ...
Samuel Shokry's user avatar
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Applications of the Kronig-Penney Model [closed]

I would like to know some applications of the Kronig-Penney Model and what parameters (effective mass, width...) are interesting to change in order to study those applications.
Elmachine's user avatar
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Measuring the effective mass

Intro: To avoid any terminology confusion, this is asked in the context of Solid State Physics and semiconductors. The canonical definition given for the effective mass is that it is related to the ...
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Does uncertainty principle apply to holes/gaps in matter?

Consider a hole in a semiconductor, or a missing atom in a crystal. Are their positions and momentum related by uncertainty principle? These factors would of course be determined by its surrounding ...
JobHunter69's user avatar
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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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9 votes
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Tunneling v. Hopping

Can someone explain the difference between hopping and tunneling? The context I'm considering is conduction in semiconductors, specifically between impurity states within the bandgap. It's always ...
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What's the purpose of capacitors in parallel

In my school textbook it is written that the capacitor acts as a filter, that is, it decreases the fluctuations in the potential difference across the load. But since all the components are ...
Akshit's user avatar
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4 answers
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Working of a p-n junction diode when forward biased

If p-type semiconductor and n-type semiconductor of a diode are equally doped, and if the diode is forward biased, then holes will move toward the n-type semiconductor and electrons will move toward ...
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6 votes
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Conduction band confusion

What actually is conduction band?I have just started learning semiconductors and this is the very first concept I am troubled with.Is this continuous energy level of all the free electrons or ...
Sharad1's user avatar
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Why are laser pulses Sech Squared in temporal shape?

Ultrashort pulses from mode-locked lasers often have a temporal shape which can be described with a squared hyperbolic secant ($\mathrm{sech}^2$) function: $$ P(t)=P_0 \mathrm{sech}^2 \left( \frac{t}{...
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Does the Fermi level change under change of temperature, voltage or other conditions?

From a previous post with similar title, (What's the difference between Fermi Energy and Fermi Level?) I think it is safe to assume that In a block of material, Fermi energy is the level, up to ...
YunliuStorage's user avatar
2 votes
2 answers
1k 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 ...
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1 vote
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Kinetic energy in the semiconductor band diagram

In Modern Semiconductor Devices (available online from the author), it's stated that "any energy above $E_C$ is the electron kinetic energy", accompanied by the figure below. Additionally, ...
Halleff's user avatar
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Semi conductors (holes and electrons)

The following relation is mentioned in my text book for semiconductors in thermal equilibrium. $$n_e ×n_h = n_i^2$$ $n_e$ stands for the number of electrons. $n_h$ stands for the number of holes. ...
Mahathi Vempati's user avatar
1 vote
0 answers
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Why does the bottom of the conduction band correspond to the potential energy of an electron?

While proving that Fermi level is constant throughout any system in thermal equilibrium, all the books I saw the proof in (for example, Sze and Shur) assume the following: the bottom of the ...
Sgg8's user avatar
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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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Why n+ contact of p type Ge is 700um thick compared to p+ contact of n type Ge only 0.3um?

Whether the reason is as follows? Predominantly HPGe is p type. So compensation of large p type impurity requires more n+ contact. (700um) But n type Ge is made by doping of excess addition of n type ...
ggs's user avatar
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How holes conduct current?

I had questions about holes in semiconductor, when i checked the net it is said holes are said to be equivalent positive charge and they say because the hole moves from one place to another when it is ...
Mohamed Osama's user avatar
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Widening of depletion region

Why does the width of the depletion region of a p-n junction diode increase when it's reverse biased by connecting it to an external voltage source?
Debasis buxy's user avatar
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Charge density in depletion layer for pn-junction

I just came across this Wikipedia article on pn-junctions: pn junction What I don't get is why the negative charge density is narrower/smaller than the positive one in Figure A. I'm guessing the ...
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Saturated BJT Transistors. V CE < V BE : AKA - Things that make you go “Hmmmm”

At the risk of being blasted for cross-posting, I am posting this question again here in the Physics department. It is a duplicate of this post in the EE forum. However, I would like to get some ...
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Is there a physical limit to data transfer rate?

Is there a physical limit to data transfer rate (e.g. for USB $3.0$, this rate can be a few Gbit per second)? I am wondering if there is a physical law giving a fundamental limit to data transfer rate,...
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