What is P-n junction: Definition and 58 Discussions

A p–n junction is a boundary or interface between two types of semiconductor materials, p-type and n-type, inside a single crystal of semiconductor. The "p" (positive) side contains an excess of holes, while the "n" (negative) side contains an excess of electrons in the outer shells of the electrically neutral atoms there. This allows electrical current to pass through the junction only in one direction. The p-n junction is created by doping, for example by ion implantation, diffusion of dopants, or by epitaxy (growing a layer of crystal doped with one type of dopant on top of a layer of crystal doped with another type of dopant). If two separate pieces of material were used, this would introduce a grain boundary between the semiconductors that would severely inhibit its utility by scattering the electrons and holes.p–n junctions are elementary "building blocks" of semiconductor electronic devices such as diodes, transistors, solar cells, LEDs, and integrated circuits; they are the active sites where the electronic action of the device takes place. For example, a common type of transistor, the bipolar junction transistor, consists of two p–n junctions in series, in the form n–p–n or p–n–p; while a diode can be made from a single p-n junction. A Schottky junction is a special case of a p–n junction, where metal serves the role of the n-type semiconductor.

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  1. prox777

    I Why diode with larger band gap has larger onset potential?

    I don't understand why voltage increases with band gap. I understand why from the equations, but not conceptually. From my understanding, the onset voltage is what is needed to overcome the contact potential that forms when the p-type and n-type samples are joined together in a p-n junction. But...
  2. rkgjet

    Space charge region of p-n junction diode

    does np=ni^2 holds even the space charge region of a pn junction diode?
  3. O

    Effect of doping concentration on the depletion width of p-n junction diodes

    My question for now is as follows: Why does a high doping concentration causes a decrease in the thickness of depletion region. Any help will be highly appreciated! Thanks a bunch Regards!
  4. Praveen1901

    B What is the purpose of the depletion region in P-N junction semiconductors?

    I'm new to semiconductors. While I was studying types of biasing in semiconductors, here's what I read - 'In forward biasing, the width of the depletion region is reduced.' Here's what I thought - Since the potential barrier is reduced in the junction due to external potential, the diffusion...
  5. S

    Wrong statement about a p-n junction

    Homework Statement A p type semiconductor is brought into contact with an n type semiconductor to form p - n junction. Which statement is false? A. During forward bias condition, if applied p.d. overcomes the junction potential, electron will cross steadily from n - type side to p - type side...

    Non uniformly distributed p-n junction related problem

    Hello guys, I stumbled upon this problem while studying non uniformly distributed pn junctions and finding difficulty solving this. Any help will be greatly appreciated. A diffused silicon p-n junction has a linearly graded junction on the p side with a = 2 x10^19 cm-4, and a uniform doping of...
  7. N

    I Drift velocity in P-N Junctions

    When a P-N junction is in reverse bias, the drift velocity of the system increases, so why is there no current flow? Is the drift velocity not connected to the current? Thanks in advance.
  8. S

    I Boltzmann Distribution: Feynman's treatment of p-n junction

    In Vol III, 14-4 and 14-5 of the Feynman Lectures (http://www.feynmanlectures.caltech.edu/III_14.html), Feynman gives a discussion of the p-n junction, in which he derives the diode characteristic equation via a nice, simple and convincing application of the Boltzmann distribution to the...
  9. Wrichik Basu

    Do carriers move across a p-n junction at 0 K?

    Often a band diagram is used to explain what happens when two pieces of the same semiconductor, one p-doped, one n-doped, are put together. I am a little confused about it, so here is my question. Initially and at ##0\mathrm{K}##, the surplus carriers should be confined to their respective...
  10. E

    The flow of electrons in a photovoltaic p-n junction

    Hi,how is the movement of the electrons in photovoltaic? I understand that there is n and p layer. What I do not understand is why the electrons does not move more directly to the p-side from the n-side. In the currect explanation it requires a circuitry. Thanx.
  11. A

    Effect of Doping on Depletion Region Width

    In an unbiased p-n junction, how does increase in doping affect the width of Depletion Region? I read somewhere that width decreases as increase in carrier concentration leads to more recombination of majority carriers with oppositely charged ions of their depletion regions leading to a...
  12. L

    Charge density in an abrupt p-n junction

    Homework Statement In an abrupt p-n junction we consider the junction between one side p-doped with ##N_A## acceptor atoms and another side n-doped with ##N_D## donor atoms. Initially the chemical potential is different in the two sides, but thermal equilibrium requires that the chemical...
  13. mertcan

    What is the derivation of built in voltage for a P-n junction?

    hi, I am looking a derivation of built in voltage, but the only thing I could find is a statement: built in voltage can be derived from band diagram with the Fermi energy constant throughout the device, or from equating the drift current through the junction equal to the diffusion current. I...
  14. W

    Why is the band offset of an LED equal to the band gap?

    I am doing an experiment where we have to use the threshold voltage of LEDs to determine Planck's constant given the following relation $$ eV_0 = E_g = \frac{hc}{\lambda} $$ where ## V_0 ## is the threshold voltage, ## \lambda ## is the wavelength of emitted light and ## E_g ## is the band...
  15. R

    Combining p-type and n-type semiconductor materials

    Hi Guys, i want to fabricate semiconductor p-type and n-type material and i want it to combine to make a p-n junction diode, but i don't know how to combine or merge the two, (my materials are thin films) I'm thinking to solder it but I'm afraid that it will break, or distort, or I'm thinking to...
  16. L

    Reverse Saturation Current in P-N Junction

    Homework Statement An abrupt Si p-n junction of cross sectional area 10-4cm-2 has the following properties: p side: number densities of acceptor impurity atoms: NA = 1017cm-3 minority carrier lifetime: τn = 0.1 us hole mobility: μp = 200cm2/Vs electron mobility: μn = 700cm2/Vs n side...
  17. B

    Short Circuit Current in Solar PV Cells

    I'm reading about short circuit current in a solar PV cell and I am a little confused. The short circuit current is defined as the current across the solar cell when there is zero potential difference across the cell. At this point the short circuit current is equal to the light current. What...
  18. D

    How do semiconductors affect a circuit?

    I understand the difference between p-type and n-type semiconductors but I just don't understand how adding a p-n junction to a circuit affects it. Can someone please explain how semiconductors work? For example, if I had a circuit with just a battery and a light bulb, what would change if I...
  19. P

    Ohmic vs Rectifying Contact: N+ & N-Type Semiconductors

    Hello Every body! As shown in below, If i join a heavily doped n+ semiconductor with an ordinary n-type semiconductor, What is the type of contact that forms between n+and n-type semiconductors ? is it Ohmic contact or rectifying contact ??
  20. S

    Dissimilar thermoelectric P-N junction materials

    Hi, I had a question about p-n junctions. I've only recently started to learn these concepts so there may be flaws in my thinking (please feel free to correct me). What I'm understanding is that for a p-n junction to function properly and produce a current when connected with a load across the...
  21. L

    What happens to the minor charge carriers in p-n junction diode

    what happens to the minor charge carriers in p-n junction diode when forward biased?
  22. M

    Photovoltaic Cell- P-N Junction Necessity

    If you wanted to separate the P and N type semi-conductive layers and place a diode (which contains a P-N junction) between them so that current would still travel in the correct direction, could you? I want to separate them so that I can insulate the N-type layer with a reflective metal. I just...
  23. F

    P-N junction voltage under polarization

    All the books that deal with the p-n junction under applied bias asume that the same equations used for the equilibrium case (no bias) can be used for the biased case provided that the juntcion voltage V_{ic} is substituted by V_{ic}-V, where V is the applied bias. Although this can seem...
  24. C

    A question on p-n junction depletion layer

    Hi, I'm studying the p-n junction and I'm a little confused about the depletion layer that forms. I understand how electrons and holes diffuse across the junction, recombine and leave charged ions but what I don't understand is why the ions remain fixed around the junction. Surely the...
  25. A

    Reverse Bias in P-N Junctions: Why Don't Electrons Diffuse Back?

    Hello! I was just having a hard time understanding how reverse bias works for a p-n junction. Put simply, why don't electrons just diffuse back into the n-type semiconductor during reverse bias, thus generating current? I was thinking maybe it's got something to do with energy levels, but I'm...
  26. M

    P-N Junction Depth: Affect on Semiconductor Device Performance

    Hi, Could anyone explain how the affect that P-N junction depth has on the performance of a semiconductor device? Are there any devices which would benefit from having a much larger junction depth?
  27. S

    Maths of carrier densities in p-n junction w/ bias.

    Hi, I'm trying to recreate some formulae of my professor's but I'm hitting a dead end. Starting with the following equation for the electron carrier density in the conduction band of a semiconductor: n = N_c exp(\frac{-(E_c - E_f)}{kt}) N_c is just a constant, E_f is the electron...
  28. V

    Recombination current in a p-n junction

    Hello all, I'm reading about rectification in a p-n junction. My book says there are two types of current for a p-n junction not in equilibrium: Generation current, and Recombination Current. Generation current Seems simple enough, but I don't get something about Recombination current. They...
  29. D

    Welcome to the P-n Junction Inquiry

    Hello. I have a question regarding the p-n junction. When I look at figure B here: http://en.wikipedia.org/wiki/P-n_junction it looks completely wrong to me. Take the E-field. It is going to be positive outside the depletion region, which in turn will make the voltage tend towards zero...
  30. A

    Why is P-N junction so important in semiconductor diodes?

    Hi, Iam having a hard time understanding the benefits of using a semiconductor to construct e.g. a photodiode that creates a current in proportion of the energy deposited by radiation. Text books says that semiconductor is preferred as detectors due to high density (larger chance for...
  31. A

    Is the P-N junction the only means to acheive a depletion region?

    Hi, I have a quick question. When constructing a semiconductor diode, the P-N junction is used to create a depletion region (depleted of mobile majority carriers) which is the active volume of the diode/detector. The region enables an electric current generated from the incomming radiation to...
  32. B

    P-N Junction Diode - Charge question

    We have been looking at P-N junction diodes in our lab session this week and investigating the current through the circuit and how this relates to the Voltage. We are using the approximation: I = (I0)*exp(qV/kT) We measured the voltage and the current for a few different voltages and this...
  33. W

    Forward bias in a silicon p-n junction diode

    Homework Statement The forward bias current I in the diode described (silicon p-n junction) varies as a function of the voltage V and temperature T described by the formula I = I_s*|e^[(|e|*V]/[n*k_b*T]) - 1| where |e| is the fundamental charge, k_b is the Boltzmann constant, I_s is the...
  34. R

    Why potential of n side is higher in unbiased p-n junction

    why the potential of n side is higher than that of the p side when no battery is connected to the p-n junction?
  35. V

    Few basic questions about p-n junction

    Hello everyone. I have a couple of questions about the depletion region in the p-n junction 1) Why don't the negative ions on p-side of the depletion region donate their respective extra electrons to the positive ions on the n-side of the region so they can both be happy (This sounds kind of...
  36. P

    Semiconductors: P-N junction and carriers density confusion

    Homework Statement Hello PF, this is my first post (however I lurked here a few times). This comes from a lab I recently did. In this lab, we measure the current and voltage at a fixed temperature, in order to make an I(V) graph of a diode. Then, from this data and equation (1), we managed...
  37. S

    Questions about the Potential and E-Field directions of P-N junction

    Hi, on re-visiting some basic ideas about PN junctions, I found I am confused with the depletion region diagram: I understand that the depletion region originated from the diffusion current at the local contact of the p and n type material, the electrons diffuse from the n type to p type...
  38. A

    Origin of the depletion region in a p-n junction

    Hi the first step to this is usually described as diffusion of electrons from the n type to the p type. However I have encountered sites and books that state that holes diffuse from p type to n type as well. I am of the opinion that only the electrons diffuse, and that there is no diffusion of...
  39. M

    How Does the Depletion Zone Affect Current Flow in a P-N Junction?

    I've been reading various explanations for a number of hours, and I'm still completely confused. I'll refer to an explanation from Wikipedia, but do point me to a better one if you know one. What does the depletion zone have to do with current flow? Looking at Figure A (see link above), there...
  40. H

    Semiconductors + p-n junction doubt

    When electrons from N region diffuse to P region, the electrons combine with holes to form a -ve negative ion leaving behind a +ve ion in P region.So, my doubt is how the holes accept the electrons and get a negative charge because as the holes are positively charged, when they accept the...
  41. M

    P-N junction charge utilisation

    Hello, A depletion region forms instantaneously across a P-N junction. When N-doped and P-doped pieces of semiconductor are placed together to form a junction, electrons migrate into the P-side and holes migrate into the N-side. As such, in the depletion region, the P-side becomes negatively...
  42. K

    Hole Diffusion Current of a P-N Junction

    Homework Statement A p+-n junction with the n-side donor concentration of 1016cm-3. If ni = 1010cm-3, the relative dielectric constant er = 12, Dn = 50cm2/s, Dp = 20cm2/s, tn = 100ns, tp = 50ns. Calculate the hole diffusion current density 2mm from the depletion edge on the n-side under a...
  43. A

    Physics P-n Junction Diode Problem

    Q:-Find the current through the resistance R in the figure:- , if the value of R is:- a.12Ω b.48Ω. Assume resistance offered by diode is 0 in forward bias and ∞ in reverse bias. Homework Equations Ohms Law:- V=RiThe Attempt at a Solution I tried using kirchhoffs law but we don't know its in...
  44. S

    P-n junction & transistors: depletion zone

    For p-n junctions (connected as a junction rectifier), the forward-bias connection (battery's positive terminal connected at the p side) results in a narrowed depletion zone, because: the p side becomes more positive and the n side becomes more negative, thus decreasing the height of the...
  45. K

    P-n junction diodes (Both bias)

    Given this picture, the circuit is put in reverse bias. Therefore the electrons are flowing INTO the p-type junction. - As electrons flow into the p-type material the depletion zone is raised as the p-side is made more negative. A picture from hyperphyics.phy-astr.gsu.edu illustrates this...
  46. D

    P-n junction in a thermoelectric device

    Greetings, I've just learned some of the basics about thermoelectrics, and I often come across a diagram that confuses me (see the third and fourth figures in the http://en.wikipedia.org/wiki/Thermoelectric_effect#Charge-carrier_diffusion"). All of the literature I've read refers to the top...
  47. S

    Full-Wave Rectifier w/ 2 P-N Junction Diodes & Transformer

    Show how two P-N junction diodes can be used in conjunction with a transformer that has two secondary windings, to form a full-wave rectifier. (Draw a circuit diagram including connections to the mains transformer). Explain the operation of your circuit using sketches of waveforms. (3 marks)...
  48. PainterGuy

    P-N Junction: connecting P-side to -ive terminal and N-side to +ive terminal

    hi everyone, i have discussed this problem with some other people but couldn't understand it well because of my own limited knowledge and understanding of such things. then i sent an email to my very dear teacher and a friend. email copy and my teacher's reply is below. now the problem is i...
  49. S

    Understanding the width of the depletion region in a p-n junction

    I am studying to become and electrical engineer and am currently taking Electronics I. I am having trouble understanding the change in the depletion region that results from a bias. I understand that at the time of manufacture the free electrons from the n-type semiconductor are attracted to the...
  50. P

    Why Can't P-N Junction Connected Series Act as a P-N-P Transistor?

    Hi I'm practising past papers however have no answers. one of the questions says: Why can a p-n junction connected in series with an n-p junction not act as an p-n-p transistor. My only thoughts were that the base element must be thin (approx 10 wavelengths of light) and in thus in this...