Questions tagged [pn-junction]
For questions about p-n junctions, which are the boundaries between p-type and n-type semiconductors and are building blocks for diodes, transistors, etc. Only use for questions about p-n junctions themselves -- do not use for questions about circuit elements that happen to contain p-n junction(s) unless the question is specifically about the element's p-n junction(s).
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Semiconductor PN Polarity
When you apply voltage to the PN semiconductor and you achieve equilibrium, why is the N side still negative (-) and P side still positive (+) when considering that all of the ions have 4 valence ...
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Minority carriers in P-N junction
Are the minority carriers (free electrons in p-type and holes in n-type) created after the doping of silicon or after the n or p side get voltage across from a power supply?
And my second question is ...
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What is the Fermi level away from the p-n junction?
I understand that the Fermi level at the p-n junction must be the same between the materials forming the junction. To achieve this, the band energies of the n- and p-type materials are bent.
However, ...
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Understanding the formula of the saturation current in a PN-junction diode
According to Wikipedia, the saturation current in a diode is given by the following formula:
$$I_S = qAn_i^2\left(\frac{1}{N_D}\sqrt{\frac{D_p}{\tau_p}} + \frac{1}{N_A}\sqrt{\frac{D_n}{\tau_n}}\right)$...
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Why does the width of the depletion region decrease with the increase in doping concentration?
Should the depletion region be increasing in width as more and more ions are uncovered at the junction due to the diffusion of majority carriers from one side of the junction to the other? Then why ...
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Drift Current Conception in PN junction
In a PN junction, under no bias, when the depletion region forms an electric current is also formed in the direction from N side to P side. This electric field, also has a potential difference, ...
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Movement of electrons and not holes in a PN junction?
So I've been clearing my concepts about the PN junction upto a deeper level today, and I've got a few questions to ask and clarify my concepts:
In a pn junction, due to diffusion, Only the electrons ...
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An accurate representation of the movement of holes in a PN junction
I want to clear my conception of the depletion region in an unbiased PN junction.
Before the formation of a depletion region in a PN junction, in the P region there is an excess of holes, aka places ...
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Contribution of hole diffusion current and electron diffusion current in a pn junction
I have recently got to learn that the hole diffusion current and electron diffusion current both point towards the N side in a PN junction? And the diffusion current is hence towards the N side.
And ...
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Drift Current in PN Junction and Barrier Voltage
I am reading this book, but the idea presented by it is very unclear.
It quotes:
However, I am not entirely convinced with the reason it provides here, like why are the minority carriers that reach ...
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Electric potential in a PN junction and the direction of electric field
Why is the direction of the electric field from N to P? Is it a standard convention?
Why are the directions of the drift current Is and diffusion current Id in their respective directions? In my book, ...
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Net current when applying an electric field to a PN junction
Can anyone explain to me that why Jn is proportional to
$$e^{-q\frac{Vbi-VD}{kT}} - e^{-q\frac{Vbi}{kT}}$$
instead of
$$e^{-q\frac{Vbi-VD}{kT}}$$
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Why is diffusion current due to p side in a diode inversely proportional to doping concentration of p side in the case of forward bias?
In a diode at equilibrium, there are Pn holes on the n side of the junction. These are maintained by the dynamic equilibrium of diffusion due to holes = drift due to holes. When a forward bias is ...
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What happens to a PN junction diode and its depletion width if forward bias voltage is greater than built-in voltage?
If the forward bias voltage applied to a PN junction diode is greater than the built-in voltage, what will happen? Will there be any depletion region? If a depletion region is still there, what will ...
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What happens when two same type semiconductiors are joined togehther?
If we join two n-type semiconductors with different doping concentrations (for example doping concentrations are 4x10^15 and 10^15 per cubic centimeter), what will happen? Will there be a depletion ...
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Layperson asking intuitive question about bipolar junction transistor
I am a layperson trying to understand how the bipolar junction transistor works from this excellent article: https://spectrum.ieee.org/transistor-history
The relevant paragraphs are as follows:
...
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What are junctions in a transistor and how does current flow in them?
I want to clarify what "junctions" are in an NPN transistor and how current flows in them.
Is the area inside the blue circle considered the "BC" junction?
According to wikipedia ...
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Why can't a P-N junction diode be used as a voltage regulator or reference in forward bias?
Usually, a Zener or avalanche breakdown region for a suitably doped P-N junction is used for voltage regulation as a substantial variation in the current (due to minority carriers) requires a ...
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PN circuit, playing with doped wafers
So I have two silicon wafers. One is P type (doped with boron) and one is N type (doped with phosphorus). I am just playing around with these and thought to myself, "can I make a diode if I ...
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Current density in an ideal PN junction diode
I found that the current density is as above.
The first question is: the logic is that when there is no external voltage applied, the diffusion current cancels the drift current. But there are four ...
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Why does the width of depletion region increase in reverse bias?
Please can you check my concepts??
Under a normal PN junction diode before connecting any batteries we know that there comes a "potential barrier" due to intermixing of holes and electrons ...
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Current versus voltage not exponential above forward voltage of diode?
I have done a simple current over forward voltage simulation for a PN diode with LTSpice.
I wonder why the curve is only exponential around the "knee-point" but it seems to be linear when ...
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How does gate-source voltage forward bias the source-substrate junction of MOSFET?
In forward bias, the p-type is connected with the positive terminal and the n-type is connected with the negative terminal.
The junction that I'm observing is the source-substrate junction. The source ...
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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 ...
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Why are quasi-Fermi levels flat across the depletion region in a pn diode under forward bias?
Why is the quasi-Fermi level flat across the depletion region in a pn diode under forward bias?
I get that EFn decreases on the p-type side and EFp decreases on the n-type side due to recombination, ...
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Majority Charge carriers and electron holes
Suppose I have an extrinsic semiconductor made of silicon and doped with phosphorous. Now, phosphorous has one more electron than silicon. After replacing one silicon atom, and taking its place, the ...
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I have some confusion in this question as two diodes and one resistance are parallel. Can anyone help?
I don't understand the concept of having two different parallel diodes.
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Voltage fluctuation due to AC in a half wave rectifier
I think I get the broader idea of using a diode as a half wave rectifier, but I have a question:
Who provides the forward voltage or knee voltage to start the diode for rectification? I am assuming it ...
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Do we operate diodes past their barrier or cut off voltage?
I think I get the idea of barrier or cut of voltage (e.g., 0.7 V for Si). So diodes start conducting after cut voltage. I have few questions for the cut off voltage
What happens if I increase the ...
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Applying voltage across reverse-biased diode
I have a theoretical question just about the internal voltage within the diode across the PN junction and how I can view that from a circuit perspective when I apply an external voltage across the ...
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(Too?) simple model of a pn junction
I want to build a simple model of a pn junction in order to show high school students how it works. I am not looking for something precise, so I use really simple discretization and I discard units. I ...
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How will new (n on n) pixel detector work at *beginning* of HL-LHC?
The pixel detector of ATLAS and CMS detector is expected to be replaced by a technology N in N, instead of N in P.
We see in the preferred answer of
In this schematic, where is the depleted layer once ...
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why diode electrons go p-n junction [closed]
The n electrons go in the p side and there are holes in n side but why it happens. they are pulled towards p side but isn't it ok that they are in their own atom ,or is it to do with atom want to give ...
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question about PN junction bias and currents in long\short diodes
I am trying to understand which current is bigger under forward bias.
The current in a short diode or in a long diode?
(with the same concentrations)
What I know is this:
So I understand how the ...
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How is the stored charge removed during reverse recovery time?
As I understand during forward bias more electrons get diffused to p side,
and more holes ...
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How does an external bias change the built-in voltage?
First things first, barrier potential/height is different than the built-in voltage of a diode. The built-in voltage is a constant. The external bias changes the barrier height. The barrier height ...
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Doesn't the forward biasing voltage have to be greater than the barrier potential for any current to be established in a pn junction diode?
I'm only talking about current conducted by the majority carriers.
First things first, barrier potential/height is different than the built-in voltage of a diode. The built-in voltage is a constant. ...
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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. ...
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LED and PN junction diode maximum frequency
I know that PN junction diodes are not used in RF mixers as they burn out due to high heat emission, for this Schottky diodes are used.
I am working on a project where I will be producing an IF of ...
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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 ...
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In this schematic, where is the depleted layer once voltage is applied to the the sensor?
In the following schematic from
https://cds.cern.ch/record/2717863/files/CERN-THESIS-2019-340.pdf
the sensor is the top part, the readout electronic is the bottom.
Once we have applied an electric ...
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Does the current change in a Zener diode if I we increase the voltage
Zener diodes work in reverse bias in the breakdown region. At breakdown voltage, high current flows. I get till here. I want to know what happens if I increase the voltage after breakdown. Is there an ...
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Why is the N side thinner than the P side in a photodiode?
I have been reading that a photodiode is built by sandwiching a very thin N type semiconductor togther with a thicker P type. Why is that so?
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Input impedances in CB and CE transistor circuits
Considering the input signal being placed across the Emitter-Base junction directly in both circuits(Common base and Common emitter), and considering this junction similar to a normal forward biased ...
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Why is the light emitted by the LED not of a single wavelength but consists of a narrow range of wavelength instead? Spectral linewidth change?
I do understand that the wavelength of the lights depends on the energy gap of the semiconductor, but why does it consist of a narrow range instead of a fixed value? is it because during recombination ...
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If a diode has capacitance, why doesn't it block the circuit after some time?
It is well known that diodes have a depletion region, which in itself has some form of capacitance due to the presence of charges on its opposite sides. In RC circuits, the capacitor always acts as an ...
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Polarity issue in JFET transistor
I'm wondering what determines the polarity conditions in a JFET - is it that this transistor can only operate when the p-n junction is in reverse biased polarization? If so, what about the states of ...
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Why is the saturation velocity for holes and electrons comparable?
In a semiconductor like GaAs, the saturation velocity for both holes and electrons is on the order of \$10^7\$ cm/s. However, under lower electric fields E, the drift velocity of electrons is much ...
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Why are the voltages the way they are in this transistor circuit?
This question is about what my book calls "transmission voltage" when an nmos is conncted to the power source, or a pmos is connected to ground. It has a hypothetical diagram ass shown:
It ...
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Semiconductors out of equilibrium
In connecting two separated materials with different Fermi levels we have carrier flow. Do electrons and holes always move in opposite directions?