Tagged Questions

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 affect it.

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How to simplify logic circuit? [on hold]

Only the AND, OR, NOT gates are there in my course and I know only how to write results including only a single of these, but my course has no mention of solving these: I just wrote ...
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2answers
26 views

Why a tunnel diode (TD) is called a diode?

Traditionally, a diode is a 2-terminal device that limits current to flow in one direction, i.e. a rectifier. But a "tunnel diode", according to wikipedia, is not rectifying: In the tunnel diode, ...
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Thermal conductivity of semiconductors - theoretical function?

Below is a plot of the thermal conductivity coefficient for Gallium Arsenide, reproduced from 3: I would like to interpolate the data, but I don't know what fit function to use. I tried a generic ...
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23 views

How does a thermistor work? [closed]

What is it about a thermistor that causes the resistance to increase as the temperature is changed? please include terms like: conduction band, forbidden band, valence band.
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15 views

Crystal structure of Silicon

From what I was reading, Silicon has a FCC unit cell but they also said that the Silicon atoms form a tetrahedron at 109 degrees from each other. Then they said that the tetrahedron is formed by ...
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17 views

Contribution of electrons to specific heat at low temperature [closed]

In nearly free electron theory, we are given to estimate specific heat at low temperatures. The first step is to set an approximation on the fraction of electrons contributing to this. ...
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1answer
28 views

Lattice and carrier temperature

If I hold a semiconductor sample at a certain temperature $T$, its lattice temperature $T_l$ will equalize: $T_l=T$. But how is this lattice temperature related to the carrier (electron or hole) ...
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1answer
38 views

Question on Shockley's equation for FETs

I'm currently studying FETs (Field Effect Transistors) in Navy school. What I know so far is that in FETs, $V_{gs}$ is reversed biased, creating a depletion zone. What this means in plain English is ...
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36 views

Why don't electrons simply diffuse back when illuminating a photodiode?

Assuming you connect the cathode and the anode with a conductor (no sources), why can't the electron-hole pairs created by the photons diffuse back instead of going through the wire? My reasoning is ...
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19 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 ...
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49 views

A question about Memristors

A question about memristors: These semiconductor entities have been defined in terms of magnetic flux leakage, and a non-linear relationship to the electric charge that has flowed. In essence, the ...
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Poisson solver diverged [migrated]

My 2D-Poisson solver is build for simulation of semiconductor. The algorithm is Gauss-Seidel iterative method. If I use simple PN junction for simulation testing, it diverged while I applied high ...
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26 views

What makes Monocrystalline silicon a good semi-conductor? [closed]

I'm researching Monocrystalline silicon for a school project and focusing on its application in Electronics. One area I'm researching is why the material is a good semiconductor, and what properties ...
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24 views

Why is the heavy/light hole band not called heavy/light electron band?

Are the bands called heavy hole, light hole and electron band, just because the charge carriers are holes/electrons or is there some deeper reason I missed? The question might seem stupid, but it ...
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22 views

Semiconductor band diagram with a doping gradient

What does the Energy band diagram in a semiconductor look like if we introduced a doping gradient? What would it look like if after we added the doping gradient we introduced an electric field? I ...
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24 views

Discrepancy in introducing Schottky barrier

I have a problem regarding introduction of Schottky barrier in metal-semiconductor junction. Because of this barrier the energies of conduction band vary discontinuously and hence the potential is ...
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2answers
52 views

Surface acoustic wave

Why does a surface acoustic wave (SAW) propagate only in the surface leyer of the solid, let's assume a semiconductor? One can create such a SAW through an interdigital transducer (IDT) as I read, ...
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1answer
66 views

Calculating Boltzmann constant using semiconductor

My task from the latest laboratory exercise in physics is to calculate Boltzmann constant from known temperature, current and voltage. We were given this circuit: By changing the resistor value, I ...
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17 views

What's so special about the invention of Blue LED that a Nobel was awarded to its invention? [duplicate]

Why was this years Nobel Prize for Physics awarded to Isamu Akasaki, Hiroshi Amano, Shuji Nakamura for inventing the Blue LED? I know that if a Nobel Prize is awarded for an invention, it must be ...
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31 views

Why in PN junctions the octet rule is dominating electrostatic repulsion?

The depletion region in PN junctions is created by charges from the N part diffusing into the P part, thus completing an octet of covalent bonds in the P part. This shift however leaves positive ions ...
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36 views

Why do we have Indirect bandgap semiconductor?

If the energy of an electron is proportional to square of the momentum k, how come we have a Indirect Bandgap material in which the minimum of the energy in conduction band is not at k not zero. P.S. ...
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1answer
48 views

Why the minority carrier lifetime is different for electrons and holes?

The lifetime of minority carriers ($\tau_n$ for electrons, $\tau_p$ for holes) represents the average time before recombination. But since an electrons must have a hole for recombination to take ...
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1answer
105 views

Has the Nobel committee mixed up this years prizes for Physics and Chemistry? [closed]

The title of the question is tongue-in-cheek but the question remains: How does the Nobel committee delineate the fields when awarding work which is of such an inter-disciplinary nature. The chemistry ...
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148 views

Nobel prize for (dangerous) LED lamps? [closed]

There are many scientific articles about the danger of LED lamps (see below from the LED magazine, from scientific american, from a governmental journal and from Harvard health newsletter): Light ...
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1answer
47 views

Why does Fermi level has a probability density of 1/2 while it may lie in the forbidden region?

I dont understand how there is a continuous probability density function in semiconductors, when there are several regions which are restricted by Energy, i.e. forbidden energies. Well i know that in ...
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18 views

Complex dielectric constant in ultraviolet range

Dielectric constant of a material could be a complex number, which is dependent of the frequency of electromagnetic wave. From the Springer material website, I learn that both the real part and ...
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20 views

Why does the width of the depletion layer in a semiconductor change with the amount of doping? [duplicate]

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 ...
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1answer
90 views

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 ...
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1answer
28 views

Size of bit cell in flash memory

If we consider a normal sd card, whose dimensions are 11x15x1 $mm^3$, there are 512,000,000,000 bits stored in 64 GB memory card. If one bit is stored per cell, size of a cell would be 10e-14 m on ...
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1answer
71 views

Why is the law of the p-n junction valid under forward bias?

I'm currently studying the physics of the PN junction. I went though the derivation of the built-in potential in the PN junction under equilibrium: $$ {Diffusion\ current\ density} = {Drift\ current\ ...
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2answers
40 views

Why is nitrogen not used as a pentavalent impurity?

I don't understand why nitrogen though a fifth group element is not used as a pentavalent impurity in doping a semiconductor.
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1answer
20 views

Can electrons move back into the donor level

In a n-type semiconductor electrons from the donor level move up into the conduction band but can they move back down? Also in a p-type semiconductor electrons move to the acceptor level from the ...
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1answer
20 views

N-type semiconductors and the number of holes?

Let us say we have Germanium which has been doped with antimony. Antinomy has a a fifth valence electron not involved in bonding. Is this electron in the valence band? I ask because all texts on the ...
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39 views

How do we predict electrical properties of a material using scattering data and vice-versa?

I know that the band gap is related to conductivity. What I'm wondering is what it is like for an experimentalist who is trying to figure out what an unknown material, a black box, is doing. The only ...
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40 views

Does the Shockley Diode Equation hold in a dynamic circuit?

Consider the following simple photodiode circuit: I've created a real-life version of this circuit, and I've detected that $I$ is oscillating: $$I(t)=I(t+\tau)\tag{$\tau\approx ...
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Silicon/silicon dioxide interface

Suppose we have an interface of silicon/silicondioxide. If we shine light on the top surface electron-hole pairs are generated in silicon. since there is always a field directing from surface to bulk ...
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19 views

What is the temperature evolution of the conductance of a quantum chaotic system?

I read this really nice article by Abanin and Levitov: http://arxiv.org/pdf/0704.3608.pdf They argued that the mixing of the quantum edge channel at the vicinity of a PN junction is described by the ...
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1answer
25 views

Why is the diffusion capacitance greater than the depletion capacitance in a p-n junction?

In a p-n junction the total capacitance is the sum of depletion capacitance and diffusion capacitance and it is mentioned that the diffusion capacitance is almost a million times greater than the ...
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1answer
40 views

why some elements of same group cannot be used for doping semiconductors?

15th group elements like As, Sb, P can be used for doping whereas N and Bi cannot be used for doping even though they too belong belong to 15th group. Why ?
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78 views

Optical absorption in a semiconductor for $E<E_g$ [duplicate]

Quoting from Solid State Electronic Devices (by Ben G. Streetman and Sanjay Banerjee): A photon with energy less than $E_g$ is unable to excite an electron from the valence band to the ...
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1answer
49 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 ...
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27 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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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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1answer
102 views

Why can't we dope the intrinsic semiconductors with sixth or second group elements?

Suppose we want to make an n-type silicon semiconductor why do we use arsenic or phosporous as an impurity? Why cant we use selinium or terellium? Infact my doubt is when we use sixth group element ...
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1answer
90 views

What factors cause the velocity saturation to occur at different electric fields for different materials?

In semiconductors the velocity of carriers gets saturated after a certain value of electric field. In silicon it occurs at around $10^4 kV/cm$ and in GaAs at some other value. What factors are ...
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1answer
18 views

How to obtain ballistic transport in a device?

I would like to know the ballistic device characteristics and illustrations (if any) to understand how can we overcome the dependence of current on carrier mobility .
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2answers
60 views

How should semiconductors be understood? [duplicate]

In the chemistry setting, a doped semiconductor is a crystal lattice with holes/extra electrons in it. In the band/quantum mechanical picture, these holes/extra electrons can be seen as the amount ...
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83 views

Diffusion and Drift currents in a PN junction

In a forward-biased PN junction, the potential barrier decreases, allowing more majority carriers from one side to diffuse to the other side where they are minority carriers. After they cross the ...
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2answers
45 views

Can the current in a semiconductor be independent of mobility of charge carriers?

Can any device be made in such a way that the current through it is independent of carrier mobility? In a usual semiconductor or a device which is made of semiconductor material the current due to ...
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2answers
84 views

What is the performance of a silicon crystal that makes it an essential component to computing

I'm on a thread of interest in the precise physics that allow the creation of the computing process. It began as a question posted in search of an understandable explanation of what physical form ...