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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Solar Cell related confusion

On interenet lot of 3D figure of solar cell. But problem is lot of variation in figures. Like: Image from Springer Nature In one figure I see light strike on side-by-side N-P regions: Image by ...
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Current density in an ideal pn junction diode

I found that the current density is as above. I am going really crazy with this problem as I can't get any clue from anywhere. I have been googling for 10 hours and have no idea. Please help. The ...
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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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3 votes
1 answer
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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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4 votes
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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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2 answers
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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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1 vote
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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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337 views

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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1 answer
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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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1 answer
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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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3 answers
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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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8 votes
1 answer
384 views

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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1 answer
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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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3 votes
1 answer
522 views

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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1 answer
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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?
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3 answers
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Explanation for drift current

My question is why the concept of drift current or movement of minority charges is necessary while the pn-junction is formed. So drift current was explained to me in more or less this way As the ...
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4 votes
2 answers
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Understanding the precision rectifier

In particular, I was trying to understand the behavior of this precision rectifier given an input wave \$V_{in}=V_{o}sin(\omega t)\$. To my understanding, the circuit reduces to what we have in the ...
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How temperature difference does not affect transistors in CPUs?

Recently I learned about semi-conductors and some devices. Today I watched a video on youtube about a guy overclocking a cpu to 7.0 ghz, while cooling it with liquid nitrogen to -192 celsius degrees. ...
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4 votes
2 answers
386 views

Is the current in reverse biased PN junction due to drift or diffusion?

Wikipedia says The saturation current (or scale current), more accurately the reverse saturation current, is that part of the reverse current in a semiconductor diode caused by diffusion of minority ...
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2 answers
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How can a tunnel diode be used as a memory element?

I read in applications of tunnel diodes that it can be used as a memory element. I am not able to justify or verify this statement. It would be very helpful if a circuit showing logic storage using a ...
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1 answer
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In the solution to this problem, why is the electron charge omitted?

The problem reads as follows: A silicon pn junction with a cross-sectional area of 10-4 cm2 has the following properties at T = 300K: n region: \$N_d = 10^{-17} cm^3\$ \$\tau_{p0} = 10^{-7} s\$ \$\...
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1 vote
1 answer
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How drift current is independent of bias voltage in semiconductors?

According to my textbook: The drift current is relatively insensitive to the height of the potential barrier. The reason for this anomaly is the fact that the drift current s limited not by how fast ...
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Why are PIN junctions better for solar cells than PN junctions?

In lecture today my professor mentioned that PIN junction make better solar cells than PN junctions. Why is this true? The PIN junction will have a wider depletion region which means it'll have a ...
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What does the fermi-level increase in reverse-bias?

Fermi-level tells us the probability of finding an electron at 50%. When you look at an energy band diagram in reverse-bias you can see the Fermi-level increases in the p-type semi-conductor. Why does ...
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2 votes
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In an energy band diagram why is the valance band in the p-type have more energy then n-type?

I am having trouble understanding energy band diagrams. In an energy band diagram of a semi-conductor during equilibrium the valence band of the p-type is higher then n-type meaning electrons in the ...
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2 votes
3 answers
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Why does a p-type conduction band have higher energy then n-type conduction band in a p-n junction?

In an energy band diagram that represents the p-n junction (during equilibrium) the p-type conduction band has greater energy then an n-type conduction band. Why does the p-type have greater energy ...
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1 vote
1 answer
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Bringing P type and N type semiconductors together in vacuum

Consider the case where a P-type semiconductor and an N-type semiconductor are placed in perfect vacuum. Now, the two junctions are brought together. In the time immediately after they are brought ...
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2 votes
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Minority carrier current in p-n junction diode

Does minority carrier current flow through p-n junction even in the absence of any external applied voltage?Is minority carrier current same as reverse saturation current?
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1 vote
1 answer
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Blocking voltage of diodes

What exactly is blocking voltage in relation with Metal-semiconductor junction diodes? Is it related to breakdown voltage?
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Are there two band contributions to diffusion current at the PN (diode) junction?

My question (I hope) is a simple one. Are there two components of diffusion current (valence band AND conduction band) contributing to the generation of the PN junction voltage? If so, do those ...
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1 vote
2 answers
212 views

Nature of conventional current flow in a p-n junction

More specifically, I'm confused about the concept of hole diffusion. I can understand that electrons diffuse towards the p-type material. However, the concept of holes diffusing is a little bit ...
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What are the typical paths of holes and electrons in an unbiased PN junction?

Can anyone tell me the typical paths of holes and electrons in an unbiased PN junction at equilibrium? In terms of diffusion currents, is that only holes (majority carriers in the the P-Type) ...
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14 votes
3 answers
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Perpetual machine from a PN-junction diode

Consider a PN junction diode Now, this system will naturally form a depletion region due to diffusion and will convert into this: Now, I wish to connect the ends of this diode with a conducting wire ...
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