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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How does base-emitter voltage affect the current gain of a transistor?

I'm doing a Physics project related to transistor operation. My data shows that as the base-emitter voltage drop increases, the current gain of the transistor rises and eventually plateaus at a ...
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46 views

Wigner-Ekhart theorem for Fermi Golden Rule in semiconductors

I have seen many authors mentioning that there is a way to work in total angular momentum basis and calculate the matrix elements using the Wigner-Ekhart theorem. Here the author even says that ...
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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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How does ambient temperature affect material conductivity

In the book I read I found many contradiction as to how ambient temperature affect material conductivity. Here is an example: Highlighted sentences are cntradictions - "Does any termal energy create ...
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51 views

Energy of an electron in the conduction band (semi conductor)

First of all, I'm using the book "Introduction to Solid-State Physics, Charles Kittel, 8th edition". At page 205, he claims that the energy of an electron in the conduction band is : $$e_k = E_c + k^2 ...
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Holes movement in p-n junction diode

Are we referring the holes movement of p-type to n-type due to the movement of valence band electrons(the covalently bonded ones) of the n-type filling the holes in the p-type under the application of ...
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37 views

Solar photovoltaic diode current flow

When the PV cell is provided an external circuit, why do the electrons flow through the wire even when it can flow directly from within, between the p and n side? What happens to the generated ...
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151 views

Where does forward voltage drop in a diode?

To simplify the picture, I would start with an n-type Schottky diode. It has two junctions: one rectifying and one non-rectifying (ohmic contact). When the diode is forward biased, it conducts ...
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383 views

What does phonon mediated absorption of photon to excite electron from valence band to conduction band mean?

What does phonon mediated absorption from valence band to conduction band mean ? Suppose we have an indirect band gap semiconductor. The excitation of an electron from valence band to conduction band ...
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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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Why is the input characteristic curve almost independent of $V_{\text{CE}}$?

I am studying the Input Characteristic curve in an $n-p-n$ transistor in common emitter configuration (high school level). My book (NCERT) gives the following curve: for this circuit diagram: I've ...
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Saturated BJT Transistors. $V_{CE} < V_{BE}$ : AKA - Things that make you go “Hmmmm” [duplicate]

We use them every day and those in the know fully understand the functional characteristics of BJT transistors. There are documents and links galore explaining the operational math. There are even ...
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2k views

Hall-Voltage behaviour with increasing temperature

I have a question relating to this diagram: It shows the relationship between Temperature and Hall-Voltage of a P-doped Germanium Plate. The electron density n is constant from 10°C to 50°C, that's ...
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Electron-hole pair recombination

Please I will like to know if a reasonable amount of heat can be generated upon the recombination of an electron-hole pair in a photo-excited semiconductor nanoparticle (such as TiO2, CeO2).
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Semiconductors : LED [duplicate]

I got to know that the threshold voltage for an LED is different for LEDs emitting different colors. I don't actually know the reason. I searched everything from the Web but didn't get that... Kindly ...
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Semiconductors : Zener Diode

I was wondering how a large current flows after a small change in the zener breakdown voltage. I know why it happens at the zener voltage, but my book says that even after insignificant change in the ...
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155 views

Semiconductors: Hole current

...And then suddenly It came in my book, Hole current is also there in semiconductors and i know it. But there's a little thing that's confusing me. Is this hole current temporary? Yes, according to ...
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Length of depletion region in pn junction

The formula to calculate the length of depletion region is: $X_{depletion}=\sqrt{2q\epsilon _{Si}(\frac{1}{N_{d}}-\frac{1}{N_{A}})(\phi _{i}-V_{a})}$ Some exercises ask me to calculate $X_{depletion}...
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P--N junction diode under zero bias

The wiki describes it as- "After joining p-type and n-type semiconductors, electrons from the n region near the p–n interface tend to diffuse into the p region leaving behind positively charged ions ...
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Is it possible to locate the Fermi level (in a double doped semiconductor) without knowing the intrinsic Fermi level?

Suppose phosphorus ($\require{mhchem}\ce{P}$) is introduced into $\require{mhchem}\ce{p-Si}$. At a given temperature (say at room temperature $300K$) is it possible to find the location of the Fermi ...
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Does Silver contact form Schottky contact for ZnO film?

In order to make a Schottky contact between metal and semiconductor material. The work function of the metal must be greater than to the work function of semiconductor material, for example, Silver (...
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206 views

Output in a half wave rectifier

In a half wave rectifier only a single diode is present. One end of the secondary wire of the transformer is connected to the p side of diode while the other to the load resistor. The n side is ...
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Point resistance

The resistance of a given object is expressed through: $$R=\rho\frac{l}{A}$$ I'm wondering if there is any quantity like resistance at a specific point. For example, $R$ for a copper wire with l=...
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103 views

Where does the factor of half come from, boltzmann distribution for bandgap energy

I have found that it is possible to calculate the conductivity of a semiconductor using the Boltzmann distribution: The source is a slideshow presentation and doesn't list much information. The ...
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Relaxation process in semiconductors

I was reading some papers on pump-probe spectroscopy of silicon. In this spectroscopy, pump pulse excites carriers(electrons and holes) from valance to conduction band and probe pulse with various ...
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How close do electrons have to be to have 'collided' within a semiconductor?

In semiconductors like Zener diodes undergoing Avalanche effect, electrons are colliding all of the time and causing a cascade that leads to current flow. So how close do the electrons have to get to ...
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171 views

Breakdown voltage avalanche photodiodes

What is the best definition to obtain the breakdown voltage of an avalanche photodiode? Update: Is it even possible to determine it graphically? E.g. by fitting a linear function or 1/x or something ...
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135 views

Incomplete ionization in a depletion region

The expression for a non-degenerate depletion region width in a pn junction is expressed as a function of Nd and Na, and Vbi, under the assumption of complete ionization of all acceptons and dopants. ...
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Wiedemann–Franz law for Copper at 100 °C

I have a colossal temperature (T)-dependent expression which has both the thermal conductivity (κ) and the electrical conductivity (σ) of copper. T fluctuates around 100$\pm$10 °C. For ...
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151 views

Why are phonons and photons orthogonal in $k$-space?

Within solid-state physics and semi-conductor theory, the band-gaps of various semiconductors are often shown using $k$-space diagrams. Within the diagram, momentum is on the $x$-axis while on the $y$-...
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346 views

Calculate steady state charge in a silicon bar after excess holes are injected

I have to derive an equation for excess hole distribution in an silicon bar injected with a steady state hole concentration $\Delta P$. I have been given the data $\Delta P = 10^{16}$ per cubic ...
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65 views

Why is LED lifetime limited? Why do they degenerate?

As I know LED is based on electrons and holes recombining in a piece of semiconductor. Emitted heat is very low. So why aren't LED's almost eternal? Why do they degenerate with time? My guess is that ...
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Is the depletetion layer of an np junction really (completely) depleted?

My confusion stems from the energy-band diagram across the pn junction (bottom of post). One the one hand, the energy levels ($E_c$, $E_v$) change continuously, on the other hand, I know that they ...
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Need help on the electrical resistances of semiconductors and metals and their dependance on temperature

So I was doing some problems and this came up : - Two resistors $A$ and $B$ having resistances $R_1$ and $R_2$ respectively at $0^{\circ}C$ and temperature coefficients $α_1$ and $α_2$ are joined in ...
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186 views

What does it mean if there's no peaks on raman spectrum?

I carried out Raman measurements of a doped semiconductor. I know what are the peaks of undoped one. I also know, that usually doped semiconductor has at least few peaks in similar positions to the ...
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227 views

Why do electrons and holes carry heat in a Peltier element?

I have read quite a lot on Peltier elements but I still can't figure out why they work exactly. Consider the following (well-made) animated diagram of a Peltier element: I think the reason why ...
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353 views

Is there a relation between density of states (DOS) and carrier mobility in semiconductors?

By changing DOS, mobility how to change? What is the relationship between DOS and mobility, if there is?
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Semiconductor: calculating effective carrier concentration

In one of the derivations of the effective carrier concentration for a semiconductor, an equilibrium $$• \rightarrow e^- + h^+$$ is considered. In this case, $$ K_c = \frac{[e][h]}{[•]c^{\circ}} = \...
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71 views

Could ballistic electron transport be used for transmission lines and undersea cables?

Ballistic conduction, from what I know, resembles superconductivity sans the Meissner effect. But unlike superconductivity it can occur at room temperature.Has there been any R&D in the use of ...
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Drift Diffusion currents in semi-conductors

Drift-Diffusion currents of holes in semi-conductors are usually written as : \begin{equation} \mathbf J_p = -D\nabla p- \mu p \nabla \phi \end{equation} Where p is the hole density, $\phi$ the ...
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Some questions regarding n and p type semiconductor

I'm learning about the band structure of semiconductors, and I learn that there're genetically two types of semiconductors .For n type semiconductor it has a shallow donor level whose electrons can be ...
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Depletion layers in undoped semiconductors

I've been studying the effects of surface states in semiconductors (in the absence of interfaces, so just semiconductor-vacuum), and am struggling with the concept of depletion/accumulation layers. I'...
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Semiconductors:LED

Given the below diagram, The text further reads why Germanium is better choice in solar cells And the next paragraph says PbS ..(ref figure) Radiation will be absorbed on top layer and would ...
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504 views

Open circuit voltage and band gap

I try to estimate the open-circuit voltage of an ideal solar cell (no non-radiative loss) with perfect absorption, illuminated by a black body at temperature $T_{\odot}$ and at full concentration. I ...
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1k views

Hall Coefficient - Is it a constant?

We did a classical Hall Effect experiment where we measured Hall Coef. given by $R_H=\frac{E_H}{J\cdot B}$. The setup was a rectangular Germanium semiconductor placed perpendicular to a magnetic field ...
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121 views

Quantum mechanics momentum matrix element

I do not manage to understand a simplification in a quantum mechanics demonstration that computes the momentum matrix element in a semi conductor band structure. In particular how to pass from first ...
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102 views

Electron density in Semi Conductors

I want to determine the relationship between the carrier density $N$ and the chemical potential $\mu_e$ in the conduction band of an intrinsic semi-conductor (GaN for example). The band structure of ...
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349 views

Flow of charges from lower to higher concentration, concentration gradient in intrinsic semiconductor

In (electronic circuits) by Neamen,it is mentioned that some charges flow lower concentration to higher concentration..Why does this happen?Also,does concentration gradient exist in an intrinsic ...
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657 views

Diffusion current in semiconductor while applying an electric field

In case of intrinsic semiconductor, while applying an electric field, only drift current should exist, right? As diffusion current is due to concentration gradient. So the electron flow will be ...
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Lack of knowledge for doped semiconductors [closed]

This question might get down votes, I presume, because it has already been asked before but I will still go for it. In terms of doped Silicon: Donor atom releases its 5th electron (and gets excited ...