All Questions
Tagged with semiconductors solid-state-devices
62
questions
0
votes
1
answer
99
views
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
views
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
views
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
views
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
views
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
views
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
views
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
views
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
$$x_{SCR} = \left[\frac{...
- 1,161
1
vote
2
answers
143
views
Why do series NMOS do better than a single NMOS from a delay perspective?
My VLSI text (Weste and Harris) writes the following:
Transistors in series drop part of the voltage across each transistor and thus experience smaller fields and less velocity saturation than single ...
- 1,161
3
votes
1
answer
270
views
What is equilibrium carrier concentration in a semiconductor? Is it material specific? How to calculate it?
Is equilibrium carrier concentration dependent on doping density? If it is, then how to know how much the doping density should be for a particular semiconductor device?
- 47
5
votes
1
answer
416
views
Semiconductors: electrons more mobile than holes despite being heavier?
I apologize if this is a very basic question. But I have always known it to be true that in Silicon, electrons have higher mobility than holes. From my semiconductor physics classes in first year, the ...
- 393
4
votes
3
answers
659
views
Potential distribution in MOSFET
Let us assume that an NMOSFET has its source, drain and substrate grounded therefore VDS and VSB=0 V . We apply a gate voltage VGS=2 V and I want to know how this potential is distributed as we move ...
- 49
0
votes
1
answer
40
views
Energy band diagram of a polar material
For a single piece of a polar material (ex. GaN, AlN, etc), there exists a constant electric field inside the material due to the bound charges at the surface.
Above figure shows the resulting band ...
- 447
2
votes
2
answers
1k
views
Why does the majority carrier concentration near the junction not decrease under forward bias? (PN junction)
We see that the current due to the majority carrier decreases near the junction as shown above, which means the majority carrier concentration should also decrease since the diffusion current is given ...
- 447
0
votes
1
answer
412
views
Derivation of microscopic Ohm's law from macroscopic version?
What I tried was:
$$\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
0
votes
1
answer
737
views
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
659
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
views
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
views
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
views
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
views
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