# 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 do i solve this Electronic question? [closed]

(a) Figure 1(a) shows a rectifier circuit. The input signal Vi is a sinusoidal waveform with peak voltage of 170 V, 50 Hz, the turn ratio of the transformer is 17:1. Assume that all the diodes are ...
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### How do I calculate the effective mass of a semiconductor $\rm InSb$?

I am trying to calculate the effective mass of the III-V semiconductor $\rm InSb$ and I am told to assume that the electron density equals the doping level, which means that all donors are ionised (...
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### Effective masses of GaAs-lattice-matched InGaAsP, using k.p method or else

For numerical simulations, I need the effective masses of electrons, light & heavy holes, and split-off carriers, in GaAs-lm InGaAsP. Alternatively, I am considering using the k.p method to ...
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### Regarding the quantum nature of floating gate transistor - tunneling, coherence, spectrum

In a floating gate transistor, the gate is electrically isolated. I have a few questions regarding the quantum nature of this device: It is sometimes mentioned that, to store or deduct charges from ...
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### Can anyone help me to solve this circuit? [closed]

Assuming the diode voltage is 0.7V, how to calculate the current flowing through the diode? And how does the earthing function in this circuit?
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### Voltage and current while operating a Zener Diode

While operating the Zener diode, even if there is a small change in the input voltage the current through the load resistance remains almost the same. Additionally, the current through the diode ...
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### What exactly is a Moiré potential in 2D materials?

Reading about 2D materials formed by transition metal dichalcogenides, I have seen that if you rotate one layer you form Moiré patterns. Apparently, these patterns produce a " Moiré potential ...
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### Why don't electrons create a hole when they leave donor atoms in n-type semi-conductors?

I have learned that in intrinsic semi-conductor when electrons leave the atom they leave a hole (that can move) . I also learned that when electrons leave the atom of a donor in n-type semi-...
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### Why isn't the positive side of n type semiconductor in diode neutralised by electrons on its own side?

In a p-n junction diode, if electrons leave the n type semiconductor, and go to the p type semiconductor and this contributes to the formation of depletion layer. But my doubt is, if we are getting a ...
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### Why energy levels of each atoms split in band theory of solid such that they are not degenerate?

I recently came across energy band theory in semiconductors and pauli's exclusion principle. But I'm not sure how energy level split and why, when the atoms are so much far from each other in solid. ...
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### What is the cause of formation of indirect band gap in semiconductors?

Background: I am an electronics (device level) student who suddenly wished to understand semiconductor stuff from basics (at solid state level, without any background in that). What I understood: From ...
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### Bound states on a Quantum Dot and Tunneling on and off the Dot

Question is essentially: How can the states on a quantum dot be bound when we can tunnel onto them? If plane wave states can tunnel onto them, these plane waves states and the 'bound' states will have ...
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### In Silicon, is visible light enough to excite most electrons from valence band to conduction band?

Valence band electrons in semiconductor may jump to conduction band if appropriate energy is applied in form of (I found the point from Samares' answer in this link and it also makes sense): Thermal ...
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### Why do the electron and hole currents vanish in equilibrium in a semiconductor?

In equilibrium, there can be no net current in a semiconductor. Accounting for both drift and diffusion current, the following relationships can be derived relating the electron density, $N_{e}$, the ...
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### How is it possible that one achieved a fundamental gap that is lower than optical gap?

I know that the optical gap is generally lower than the fundamental gap, but when is the optical gap is lower than the fundamental gap?
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### What does intrinsic and extrinsic contribution to Hall effect mean?

In the context of transportation theory (electron and thermal conductivities), what is the physical meaning of extrinsic and intrinsic contributions to the Hall effect (i.e. transverse conductivity)? ...
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### Quasi-Fermi levels, can this condition be false?

Let $E_{FV}$ be the Quasi-Fermi level of the valance band, $E_{FC}$ be the Quasi-Fermi level of the conduction band and $E_g$ be the band gap (the energy difference between valance and conduction band)...
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### Cut-off frequency of an LED [closed]

I'm trying to solve this problem: A GaAs LED is at $300 K$ when the current density is 100 $A/cm^2$ . The width of the active region is $1 µm$. Assume that, for that current, we are in the strong ...
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### The calculation of effective mass for silicon

From what it was written, the calculation of effective mass in semiconductor had two different types, one is effective mass for density of states, through geometrical mean, the other one was the ...
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### Shockley diode equation - temperature influence

when looking at Shockleys ideal diode equation I wonder what "meaning" the temperature has in there? If I assume $$I(T) = I_0 \left(\exp \left( \frac{U}{k_BT/q}\right)-1 \right)$$ and vary ...
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### Short circuiting a PN semiconductor device

Consider the potential distribution across a PN junction. The difference in the Fermi levels between the differently doped semiconductors leads to a 'built-in' voltage across the semiconductor ...
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### How does Oxygen influence band gap in Silicon Suboxides?

I just started to study about Mott’s Formalism and as I was going through some prerequisite material for Variable-Range Hopping Conduction I read the following paragraph, " Theories on non-...
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### What is the light line or light cone and how is related with total internal reflection and snell law?

I'm have been reading about light propagation in periodic dielectrics. And in one part they introduce the light line. They mention that whenever the parallel and vertical components of the wave vector ...
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### Why do photomultiplier tubes (PMT) require high voltage but silicon photomultipliers (SiPMs)/semiconductor photodiodes use low voltage for operation?

I have a PMT that requires 1000V for operation, but SiPMs, semiconductor photodiodes require only about 30V -- what fundamental feature causes this vast difference in operation bias?
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### When can we neglect the effect of diode capacitance?

I was told that for DC and low-frequency AC circuits, the effect of diode capacitance can be neglected. The model of the diode of concern here is that which represents the diode as a current source ...
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### How does doping affect the color of a semiconductor?

Does P/N doping a semiconductor affect the color in some straightforward manner? Say the material starts as a yellow color and it is p doped, what can we expect from this information or what ...
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### Electronegativity in superconducters

What role if any does electronegativity have in superconductors. Most of the elements used in superconductors on the periodic table are at the low end of electronegativity and I was wondering if there ...
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### Mobility of electrons vs holes in semiconductors (intrinsic vs extrinsic)

I was reading my class notes and it was written that electrons are more mobile than holes because the effective mass of electrons are lower than that of holes. (μ=eτ/m*) I checked online to find the ...
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### What affect longitudinal conductance but not hall conductance in semiconductors

Hi as a general question, what mechanisms (e.g. impurities) affect σxx but not as much σxy in a semiconductor system at low temperature with impurities. I know with electric field scattering induced ...
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### Why does solar cell performance use short-circuit current per unit area and open-circuit voltage without reference to the cell area? [closed]

Here on this slide on page 54: Only the short-circuit current ($J_{SC}$) is given with respect to area, whereas the voltage stands without relation to area. One could calculate it, because the area ...
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### Why does Ashcroft and Mermin say an acceptor level in a semiconductor cannot be empty, only singly or doubly occupied?

On page 581 of Ashcroft and Mermin, Solid State Physics: Acceptor Level In contrast to a donor level, an acceptor level, when viewed as an electronic level, can be singly or doubly occupied, but not ...
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### Limits of integration on density of states in semiconductor

The density of electron states in a 3D semiconductor is given by $\rho(E)=\frac{1}{2\pi^2}\left(\frac{2 m^*}{\hbar^2}\right)^{3/2}\sqrt{E}$, derived commonly as shown here. I'm trying to understand ...
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### What is the physical meaning behind negative slope of laser characteristics?

Sometimes I measure LIV curves of many semiconductor lasers with the same material and width and different cavity length. There should be positive slope and intercept of Threshold current vs inverse ...
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### Why is n-p-n transistor typically “faster” than p-n-p transistor?

I know that the n-p-n transistor is faster than p-n-p transistor. My book explains it with 'the hole is faster than an electron. But I think the hole is empty space of electron, so these speeds should ...
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### Energy of exciton formation in semiconductors

Many sources I've seen have alluded to: An exciton can form when a material absorbs a photon of higher energy than its bandgap I looked at absorption enhancing effects of excitons, and am aware of ...
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### How does forward biasing of both junctions in BJT leads to saturation?

As far as I know, for an NPN-BJT, when both (base-emitter and base-collector) are forward biased; we consider the operation to be in saturation mode. Here, the transistor functions as a short circuit ...
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### What is the relation between the short-circuit current and the band gap energy in solar cells?

For the VOC it is: VOC = E_g - something, where something is positive and depends on the Urbach energy. Otherwise it should be linear: https://aip.scitation.org/doi/pdf/10.1063/1.49397 For the ISC I ...
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### How many hot electrons are in solar cells that do not thermalize?

When an electron in a solar cell is excited beyond the conduction band edge, it will most likely thermalize which can only be counted as a heat loss. But in a few cases the electron will directly ...
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### Is Collector current depends on width of base and Vcb in forward active mode? (common base transistor)

I asked this question on electronics.SE but I don't get any good answer may be because its more of a physics question . I just started reading about transistors from book "Microelectronics ...
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### Why don’t illuminated series connected (photo-)diodes bias each other?

When you connect, let's say, three photodiodes or solar cells, with a load, and you measure the voltage across the middle photodiode. Will the voltage change if the adjacent cells are in the dark if ...
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### Finding a constant in nonparabolic dispersion relation in conduction band

The dispersion relation for a semiconductor is $$\frac{\hbar^2 k^2}{2m^*}=\sqrt{\alpha E+E_g^2}-E_g$$ where $E$ is the energy from the conduction band edge, $E_g$ is the bandgap energy, $m^*$ is the ...
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### Conductance of an interacting quasi one dimensional wire using the method for a 1D Fermi gas?

Assuming the electrons are non interacting and spin degenerate, the conductance of a quasi one dimensional quantum wire is quantised in units of $2\frac{e^2}{h}$. For small voltages, we simply count ...
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### Why can it be important to engineer band alignments/offsets (e.g. CdS buffer layer in CIGS)?

I would like to ask this question by the example of the CdS buffer layer in CIGS solar cells. One paper (https://pubs.rsc.org/en/content/articlelanding/2017/se/c7se00348j#!divAbstract) says that CdS ...
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### Why is the diffusion length defined for minority charge carriers only?

As far as I could infer from the solar cell literature, when talk is about the "diffusion length", only the minority carriers are concerned. Is there a diffusion length defined for majority ...
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### Why are we even interested in solar cells under bias voltage?

I couldn't find any answer on this super basic question. Some people on the internet say that you would not put a solar cell in an array under bias, others say that they bias themselves, but I don't ...
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### Effective density of states $N_c$ at different temperature for $\rm Si$

For Silicon at room temperature, Nc = 2.8x10^19 per unit volume. For 300K, m*/m = 1.81 for Silicon. Now Nc is proportional to 1.5th power of both temperature and m* (effective mass). So, at any other ...
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### Are solid-state windmills feasible? [closed]

Imagine a structure exposed to wind. It is designed chemically so that a molecule striking the surface can transfer kinetic energy to electrons that are promoted to a higher energy state. These move ...
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### Is Making a laser diode at a home workshop impossible?

I love to play with laser diodes and they have always been a fascinating thing for me. Usually, I play with $0.1$mW laser diode pointer (Which are just toys) . From some physics textbooks and videos , ...