All Questions
Tagged with semiconductors solid-state-devices
62
questions
0
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1
answer
99
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Process compatibility between a non-planar avalanche photodiode and planar CMOS at 0.130μm process technology node
I plan to integrate a non-planar P⁺⁺/i/P⁺/N⁺⁺ avalanche photodiode (APD) array with a peripheral control circuit (e.g., trans-impedance amplifier, analog-to-digital converter, and quenching circuit) ...
1
vote
2
answers
85
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Why does light doping imply a large temperature coefficient?
In a discussion about how one can make integrated resistors in a given IC technology, Gray, Hurst, Lewis, and Meyer (Analysis and Design of Analog Integrated Circuits) remark that if we want to use a ...
- 1,161
1
vote
1
answer
67
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Limit of applicability of "quasistatic"/capacitive picture of devices
When analyzing the transitories associated with switching in semiconductor devices, in textbook treatments one often sees the time dependence considered by including (potentially nonlinear) capacitors ...
- 1,161
1
vote
1
answer
122
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Why doesn't side diffusion raise resistance of an integrated resistor?
Consider forming an integrated resistor by diffusion of n+ dopants down into some p- substrate (the corresponding pn junction is reverse biased during operation). Let \$W,L,t\$ be the width, length, ...
- 1,161
4
votes
2
answers
838
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Why are drain and source not actually perfectly symmetric?
In textbook treatments, one has that the source and drain of a MOSFET are completely symmetrical and therefore interchangeable -- the distinction is only made by which is at a higher voltage in the ...
- 1,161
0
votes
1
answer
114
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Understanding thermal instability breakdown in pn junctions
I am currently reading Sze (Physics of Semiconductor Devices, 3e, Chapter 2.4.1) and am trying to understand his discussion of thermal instability breakdown/runaway in pn junctions. I have also ...
- 1,161
3
votes
1
answer
221
views
Why do PMOS suffer a worse body effect than NMOS?
Gray, Hurst, Lewis, and Meyer give the following discussion around PMOS transistors which I followed except for the sentence which reads:
Good use can be made of this fact in analog circuits to ...
- 1,161
1
vote
1
answer
100
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Confusion about why pn junction discussion insensitive to doping variations faster than Debye length
Sze (Physics of Semiconductor Devices, 3e) gives the following discussion which relates to how equilibrium electric fields/equilibrium potential build-up at thermal equilibrium are related to doping ...
- 1,161
0
votes
1
answer
88
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Does \$\phi_{bi}\$ depend on applied voltage in non-uniformly doped junctions?
Consider a linearly graded junction
$$N_D - N_A = ax$$
for some grading constant \$a\$.
Using the standard simplifying assumptions one finds that the depletion region extent is
$$x_{SCR} = \left[\frac{...
- 1,161
1
vote
2
answers
143
views
Why do series NMOS do better than a single NMOS from a delay perspective?
My VLSI text (Weste and Harris) writes the following:
Transistors in series drop part of the voltage across each transistor and thus experience smaller fields and less velocity saturation than single ...
- 1,161
3
votes
1
answer
270
views
What is equilibrium carrier concentration in a semiconductor? Is it material specific? How to calculate it?
Is equilibrium carrier concentration dependent on doping density? If it is, then how to know how much the doping density should be for a particular semiconductor device?
- 47
5
votes
1
answer
416
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Semiconductors: electrons more mobile than holes despite being heavier?
I apologize if this is a very basic question. But I have always known it to be true that in Silicon, electrons have higher mobility than holes. From my semiconductor physics classes in first year, the ...
- 393
4
votes
3
answers
659
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Potential distribution in MOSFET
Let us assume that an NMOSFET has its source, drain and substrate grounded therefore VDS and VSB=0 V . We apply a gate voltage VGS=2 V and I want to know how this potential is distributed as we move ...
- 49
0
votes
1
answer
40
views
Energy band diagram of a polar material
For a single piece of a polar material (ex. GaN, AlN, etc), there exists a constant electric field inside the material due to the bound charges at the surface.
Above figure shows the resulting band ...
- 447
2
votes
2
answers
1k
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Why does the majority carrier concentration near the junction not decrease under forward bias? (PN junction)
We see that the current due to the majority carrier decreases near the junction as shown above, which means the majority carrier concentration should also decrease since the diffusion current is given ...
- 447
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votes
1
answer
412
views
Derivation of microscopic Ohm's law from macroscopic version?
What I tried was:
$$\overrightarrow{E}= - \triangledown V \qquad \qquad\qquad\qquad (1) $$
$$V= IR\qquad \qquad\qquad\qquad\text{(Ohm's law for materials where V}\propto \text{I)}$$
$$\text{...
0
votes
1
answer
800
views
Given a energy band diagram, can you always calculate potential, electric field, and charge distribution?
Given a band diagram, where do you start to get the electric field and charge distribution?
- 447
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1
answer
737
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Electric field of Schottky diode
Reference: Device Electronics for Integrated Circuits 3rd Ed. Richard Muller
I am trying to understand how to calculate the maximum electric field. The answer given in the book is $$E_{max} = \frac{-q ...
- 447
0
votes
1
answer
658
views
Why does the value of shunt resistor need to be very high for solar cell's greater efficiency?
In the circuit equivalent of a solar cell, shunt resistor is described as "The irregular polycrystalline lattice grain boundaries that resist to the flow of electrical current in the silicon ...
1
vote
1
answer
3k
views
Why does channel length modulation only occur in the saturation region?
As drain voltage is increased, the reverse bias across the drain-body junction also increases and thus the width of the junction should also increase which should deplete the channel length as well. ...
- 469
2
votes
1
answer
474
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Is saturation region defined for a "given" collector emitter voltage?
I have seen the traditonal saturation regions graphs (attached). The graph gives the impression that there is a huge region which is saturation region. Shouln't the saturation region be for a "...
- 271
0
votes
3
answers
1k
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Does the collector voltage have to be greater than the emitter voltage by few tenths of a volt for an NPN transitor
For an NPN transistor, does the collector voltage have to be greater than the emitter voltage by few tenths of a volt for it to be in active state? If yes what is the reason?
Also it says greater by a ...
- 271
2
votes
0
answers
57
views
How does the stored charge gets decayed when going from forward bias to zero bias?
In a pn junction diode when forward biased, excess electrons and holes get stored in p and n regions respectively.
If we short the diode by connecting p,n terminals with a wire,
how do these stored ...
- 1,150
0
votes
2
answers
843
views
Relation between forward bias and current in a diode
I have seen the VI graph to depict the relationship between forward bias and current. (left graph) and I think I get it. I have also seen another graph (right graph) to depict the relation between ...
- 271
1
vote
2
answers
1k
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How can a Zener diode maintain a constant voltage?
A Zener diode in reverse bias more than breakdown starts conducting. If you increase the reverse bias:
It conducts more i.e current in it increases
The voltage across it remains same
I think I get ...
- 271
2
votes
1
answer
993
views
What is the exact meaning of 0.7V voltage drop in a forward-biased diode?
this question is partially (but not totally) discussed here:
Why do diodes have a voltage drop?
Does the power drop on a diode become entirely heat?
The conclusion is that, in a forward-biased diode ...
- 3,550
0
votes
1
answer
72
views
How to convert spontaneous emission into stimulated?
I have a semiconductor diode that has spontaneous emission (LED).
The question is what can I change in the fabrication of the diode to improve its performance such that the diode gains a stimulated ...
0
votes
0
answers
61
views
MOSFET current at very low temperature (4K)
I am trying to model the current at low T. To do so I need to compute the integral between the fermid diract statistic and the conductivity, with respect to energy. My problem is that I cannot ...
- 1
0
votes
0
answers
46
views
What is the structure of GaAs?
Ga has three valence electron, and As has five valence electron. How do they share electrons so that each has 8 valence electrons? Does each Ga atom share 5 electrons with 5 different As atoms?
- 447
1
vote
1
answer
374
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Does hole concentration fall below the intrinsic concentration, if Si is doped with pentavalent impurities?
If we increase N type doping in a pure Silicon then according to the equation
$$P_n=\frac{n_i^2}{N_D}\text.$$
Then mathematically, hole concentration is less than \$n_i\$, if \$N_D>n_i\$.
Why does ...
- 49
0
votes
0
answers
27
views
direction of current densities for electrons and holes?
Let's say we have:
\$ J_n = 3 \frac{A}{m^2} \$ and \$ J_p = 2 \frac{A}{m^2} \$
and let's define the direction of positive current (flow of positive charges) to be moving from left to right. Then, ...
- 447
-1
votes
1
answer
87
views
Does solar cell absorb sub-bandgap photons?
My understanding is that although we are taught that solar cells only absorb photons of energy higher than the bandgap of the material, some of the sub-bandgap photons still gets absorbed, which is ...
- 447
0
votes
1
answer
266
views
Dielectric constant (relative permittivity)
I recently learned that the dielectric constant (or relative permitivity) is not actually a constant, but it depends on wavelength or frequency (dielectric function). If that is the case, why are we ...
- 447
1
vote
1
answer
158
views
Does the Shockley Ideal diode equation involve drift current?
I've encountered a contradiction in semiconductors.
The ideal diode equation considers saturation current (the current when applied voltage is reverse biased to the diode). I thought that saturation ...
- 925
1
vote
0
answers
246
views
Semiconductor mass action law question
I was told that the mass action law $$np = n_i^2$$
only applies to compensated semiconductors and intrinsic semiconductors, and it does not apply to n-type or p-type semiconductors. Is this true? I ...
- 447
1
vote
0
answers
47
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Can anyone properly explain me the characteristic curve of the p-type JFET?
I know how a MOSFET works. But recently I wanted to know details about JFET.
When V(GS) = 0 volts there will obviously a current flowing through the p-type channel. What confuses me is how the ...
- 2,519
0
votes
0
answers
43
views
Short Channel MOSFET model
I was reading on a book (Thomas Lee, The Design of CMOS Radio Frequency Integrated Circuits) that in a short channel model, since the phenomenon of drift speed saturation is very relevant, it is a ...
- 3,550
0
votes
0
answers
215
views
Why is the absorption coefficient (α) not zero for energy of incident photon less than the band gap of the semiconductor?
α ( Absorption Coefficient) tells us about the absorption of a photon by a semiconductor for the creation of electron-hole pairs.
The absorption coefficient increases abnormally as the energy of ...
- 35
3
votes
0
answers
135
views
High frequency switching applications
I was reading that for high frequency switching applications with
semiconductors, the ratio of the electron to hole mobility should be high.
Why is it so? Is it a necessary condition always? Or ...
- 171
1
vote
2
answers
449
views
Why conductivity increases in semiconductor when doped?
I know it depends upon the concentration of electrons and holes . So if we add donor atoms, even though electron concentration in conduction band increases , hole concentration decreases due to more ...
- 469
1
vote
1
answer
136
views
Why in semiconductor studies, we are only concerned with reduced zone representation of e-k diagram?
Does electron transition from conduction band to valence band takes place only in first Brillouin zone? Or can it happen in any other Brillouin zone?
- 469
0
votes
1
answer
215
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Why carriers move when Electric field is applied on Haynes-Shockley experiment
I would like to know why excess carriers/minority move when an electric field is applied at the Haynes-Shockley expirement
2
votes
1
answer
605
views
Confusing regarding measuring barrier potential of a pn junction using a voltmeter
I have been trying to understand why we can't measure the Barrier potential existing in an unbiased pn diode but on seeing the answers I am quite confused.
There seems to be two answers to this ...
- 469
0
votes
1
answer
115
views
on-state voltage
I am trying to study an ever-on IGBT. in other words, IGBT is tried to be on in a long time. To this purpose, a +15V constant dc voltage is applied to the gate-emitter. But, when connecting a +2V ...
- 49
0
votes
1
answer
345
views
MOS Capacitor Band Edges
I am trying to understand the MOS-Capacitor band edge shapes. When negative voltage is applied for gate, why does the band edge across the insulator shift upward (and linear decreasing band edge)? ...
0
votes
2
answers
177
views
semiconductor equilibrium and steady state
Why should equilibrium imply steady state? For example, there is a process whose rate increases with time and this process can be exactly balanced by an inverse process whose rate also increases with ...
- 21
0
votes
1
answer
182
views
Electrons and Holes in a semiconductor
In an exercise I have an un-doped silicon I find that p=1.80e+11 ,n=6.60e+10 , should the numbers be more close to each other? (for example in GaAs I find 1.10e+14 and 1.60e+14)?? (also p number of ...
3
votes
1
answer
694
views
Why is Junction Temperature called so?
Why is the silicon die temperature inside a semiconductor device referred to as "Junction" Temperature ?
Though this name may make sense for minority carrier devices where there is maximum power ...
- 249
2
votes
1
answer
851
views
Difference between Vth and Vge?
What is the difference between the threshold voltage (Vth) and gate-emitter voltage (Vge) for IGBT devices?
How can I calculate Vth of an IGBT chip?
- 21
0
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1
answer
131
views
Temperature-Dependent Electrical resistance Si and SiC
In a power electronics device, it seems that silicon carbide (SiC) has a higher variation of electrical on-state resistance with temperature in comparison to silicon (Si). Does anybody know the reason?...
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