Skip to main content

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).

Filter by
Sorted by
Tagged with
0 votes
1 answer
37 views

Why don't LED datasheets specify a maximum rated voltage?

I understand that (i) LED's have forward voltage drops (Vf) and (ii) that exceeding the dissipation wattage or max current can damage the device; thus one uses a series resistor to limit the current. ...
KJ7LNW's user avatar
  • 2,056
1 vote
0 answers
52 views

How fast and far do electrons move in a diode during reverse bias?

When I have looked at videos on how diodes work, they make it seem like the electrons move extraordinarily quickly during reverse bias and quite a bit to expand the depletion regions. However, I would ...
John's user avatar
  • 11
0 votes
0 answers
59 views

Why does photodiode junction capacitance affect operating bandwidth? (from a semiconductor physics model perspective)

Here is a typical equivalent circuit diagram of a photodiode. I feel like this circuit model broadly makes sense to me. You have a diode, in parallel with the junction capacitance. The photocurrent ...
genericpurpleturtle's user avatar
1 vote
0 answers
48 views

Junction diode "built-in" voltages

When a PN Junction terminal are left open-circuited, the voltage measured between then is zero. The Junction voltage Vo does not appears. Because similar built in voltages arise at metal semiconductor ...
Abdus Salam Akand's user avatar
0 votes
1 answer
45 views

How to best relate a case temperature measurement with the actual junction temperature?

If I have 4W of power dissipated through a transistor (as derived from measured current and the datasheet's on-resistance) and I measure 40 deg. C on the case of the transistor, what is the best way ...
plu's user avatar
  • 713
1 vote
1 answer
153 views

Reverse current in diodes

I'm getting started with electronics and couldn't help but wonder about this: When the PN junction diode is reverse biased (P connected to the negative terminal and N connected to the positive ...
Santhosh S's user avatar
1 vote
1 answer
114 views

Non-Schottky SiC diodes

Hopefully this isn't too much of a shopping question. I am looking for off-the-shelf silicon carbide P-N junction diodes, but all I can find are Schottky ones. Do P-N version ones even exist ...
user1402154's user avatar
0 votes
1 answer
61 views

Clarification on Diode Recovery Times and Conduction State

I have a diode in my circuit with reverse voltage of 100 V and forward voltage of 2 V. It experiences a reverse voltage of 100 V and immediately the voltage changes to 10 V in forward direction so it ...
MohammadAli Zeraatkar's user avatar
0 votes
1 answer
113 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 ...
EE18's user avatar
  • 1,161
1 vote
1 answer
98 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 ...
EE18's user avatar
  • 1,161
0 votes
2 answers
87 views

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 ...
同等の構成's user avatar
1 vote
2 answers
516 views

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 ...
同等の構成's user avatar
0 votes
1 answer
85 views

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, ...
GingerBadger's user avatar
1 vote
1 answer
569 views

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)$...
Surzilla's user avatar
  • 121
0 votes
1 answer
305 views

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 ...
SubbSE's user avatar
  • 23
1 vote
2 answers
397 views

Drift Current Concept 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, ...
SubbSE's user avatar
  • 23
0 votes
2 answers
158 views

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 ...
SubbSE's user avatar
  • 23
0 votes
2 answers
86 views

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 ...
SubbSE's user avatar
  • 23
0 votes
1 answer
106 views

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 ...
SubbSE's user avatar
  • 23
0 votes
1 answer
50 views

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 ...
SubbSE's user avatar
  • 23
0 votes
1 answer
158 views

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, ...
SubbSE's user avatar
  • 23
4 votes
2 answers
126 views

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 $$e^{-q\frac{Vbi-VD}{kT}}$$
South goodman's user avatar
3 votes
1 answer
101 views

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 ...
Joel Varghese's user avatar
1 vote
0 answers
60 views

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 ...
Wanderer's user avatar
  • 179
1 vote
0 answers
31 views

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 ...
Wanderer's user avatar
  • 179
0 votes
2 answers
198 views

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: ...
Bob's user avatar
  • 103
0 votes
2 answers
228 views

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 ...
Dan's user avatar
  • 557
7 votes
5 answers
2k views

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 ...
ThePhysicist's user avatar
1 vote
0 answers
45 views

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 ...
CakeMaster's user avatar
0 votes
1 answer
2k views

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 ...
abouttostart's user avatar
0 votes
1 answer
582 views

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 ...
Damstridium's user avatar
3 votes
1 answer
263 views

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 ...
Junius's user avatar
  • 1,041
0 votes
2 answers
1k views

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 ...
Simone's user avatar
  • 133
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 ...
user207787's user avatar
5 votes
2 answers
4k views

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, ...
user207787's user avatar
1 vote
1 answer
110 views

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 ...
Nakshatra Gangopadhay's user avatar
2 votes
2 answers
308 views

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.
Sudipta Progga Islam's user avatar
0 votes
1 answer
208 views

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 ...
user31058's user avatar
  • 271
0 votes
3 answers
166 views

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 ...
user31058's user avatar
  • 271
0 votes
0 answers
461 views

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 ...
jaurunjljgrtutkwcy's user avatar
1 vote
0 answers
73 views

(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 ...
courno's user avatar
  • 111
2 votes
1 answer
91 views

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 ...
Mathieu Krisztian's user avatar
1 vote
2 answers
59 views

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 ...
Aamirshah SHAIK's user avatar
1 vote
0 answers
372 views

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 ...
bitmetvt's user avatar
4 votes
2 answers
745 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 ...
across's user avatar
  • 1,150
0 votes
0 answers
186 views

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 ...
tryingtobeastoic's user avatar
0 votes
1 answer
893 views

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. ...
tryingtobeastoic's user avatar
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. ...
Souhardya Mondal's user avatar
-2 votes
1 answer
267 views

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 ...
shafik's user avatar
  • 59
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 ...
across's user avatar
  • 1,150