What is Junction: Definition and 223 Discussions

A junction, in the context of rail transport, is a place at which two or more rail routes converge or diverge. This implies a physical connection between the tracks of the two routes (assuming they are of the same gauge), provided by points (US: switches) and signalling. Junctions are important for rail systems, their installation into a rail system can expand route capacity, and have a powerful impact upon on-time performance.

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  1. Corwin_S

    Maximum Built-In Voltage of a PN junction

    Hi, I'm familiar with the expression for calculating the built-in voltage of a p-n junction. How can I find the maximum built-in voltage before the semiconductor becomes degenerate (i.e., a bad metal) if I only know the material and the intrinsic carrier concentration at a given temperature...
  2. cnh1995

    Built-in voltage of pn junction diode

    Why can't the built-in voltage of diode be measured by a voltmeter when the diode is isolated? A potential difference of almost 0.7V exists at the junction, which is clearly not too small for the voltmeter to detect. What's the reason?
  3. N

    From where we measure current in a pn junction diode

    Please anyone explain me from where we measure current or we apply ammeter in a pn junction diode to measure current
  4. Amal Thejus

    Static or Dynamic equlibrium in a PN junction?

    Homework Statement We are considering an UNBIASED junction.[/B] I've read in a textbook that electric field created in the junction STOPS diffusion BUT in the same text its written the drift and diffusion currents cancel each other. 1. Does the diffusion and drift currents occur simulataneously...
  5. P

    PN Junction: Current flow in Reverse Bias

    Can someone explain why after a certain voltage, current flows. We were taught that in pn junction when a reverse voltage is applied the depletion region grows wider. Using this no matter what the voltage current should not increase. So why does a current flow when a reverse current is applied.
  6. Amal Thejus

    Why there is NO current in a PN junction under equilibrium

    Homework Statement Its said that there is no Net current in a PN junction under equilibrium as the drift and diffusion currents cancel each other. We are talking about a Step junction at equilibrium. Homework Equations Its just a qualitative analysis. 3. The Attempt at a Solution [/B] The...
  7. Amal Thejus

    Variation of Potential outside a PN junction

    Homework Statement 1. We are considering a step junction at equilibrium(no external voltage applied). 2. The potential variation is shown as negative potential at P region(which is shown as constant) and increasing through the transient region to become positive in the n region. Homework...
  8. Amal Thejus

    Variation of Potential outside the PN junction

    Homework Statement 1. We are considering a step junction at equilibrium(no external voltage applied). 2. The potential variation is shown as negative potential at P region(which is shown as constant) and increasing through the transient region to become positive in the n region. Homework...
  9. Robin_Shorrosh

    Exploring Quantum Computing: Making a Qubit with Josephson Junctions

    I am working on a project for our local science fair and decided on researching quantum computers. (This is what my focus will be in college.) Though, I expect to work on this far past the time allotted for that. I would like to build a superconductor based qubit using Josephson Junctions. The...
  10. D

    Does any current flow in reverse PN junction?

    Homework Statement Homework Equations [/B] When a diode is reverse biased positive donor ions are left in the N semiconductor and negative acceptor ions in the P type. And since the N is conected to + and its donnor ions has a large +charge, why no electrons from P cannot cross the junction and...
  11. D

    Why Don't Electrons Flow from P-type to N-type in a Reverse Biased PN Junction?

    [Mentor's Note: Thread moved and edited by mentor.] Sorry I am new and I had problems creating the thread. But I will post my question here:-D. So in reverse biased pn junction the width of the depletion layer increases. But on the N side a large positive charge from the donnor ions is...
  12. F

    Kirchhoff's Junction Rule in the AC case....

    Kirchhoff's laws are valid for DC circuit and also for AC circuits (up to point. I think they become only approximations at high frequencies). Let's consider a node (junction) in a AC circuit. Three AC currents with the same magnitude but different relative phases enter the node. It is possible...
  13. A

    Bipolar Junction Transistor

    Does the collector current in a transistor depend on the base-collector voltage in a common base configuration? If so,how does it depend mathematically?
  14. R

    Liquid junction potential in Weston cadmium cell

    Liquid junction potential occurs when 2 solutions of different concentrations are in contact with each other. The more concentrated one would have tendency to diffuse faster comparitively than less concentrated. The rate of diffision depends on the mobility of ions. Weston cadmium cell is...
  15. F

    Bipolar Junction Transistor and CPU

    I am looking at the Bipolar junction transistor, but I cannot seem to correlate with how the design would work for the CPU in terms of 0 and 1s. I am looking mainly at the transistor diagram from Wikipeida https://en.wikipedia.org/wiki/Transistor. Can someone tell me what Vcc, Vin, and Vout are...
  16. L

    Josephson Junction Demo: Why Is It Called 'Frequency'?

    Very interesting demonstration. I am not sure why some authors call that Josephson junction frequency Josephson plasma frequency? If we put some radiation as in 3:45 in the video does that frequency needs to be equal as Josephson junction frequency in order to get ac characterstic?
  17. G

    Drift current of a PN junction

    The magnitude of a drift current density is given by J = qnv, where q is the carrier charge, n is the carrier density per unit volume, and v is the carrier drift velocity. q is a physical constant and n is independent of bias. But when an external electric field is applied, the minority charge...
  18. Sayani Ghosh

    Schottky junction solar cells

    I was wondering in Schottky junction solar cells, how is the open circuit voltage dependant on the built in potential and the Schottky Barrier Height?
  19. M

    What is the Junction Equation for this Circuit?

    Homework Statement I can't tell what the junction equation is for the following circuit. To me it looks like I3=I1+I2+I4 but I'm not sure. Homework EquationsThe Attempt at a Solution
  20. 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...
  21. Y

    Origin of current phase relation in Josepshon junction.

    At the superconductor-superconductor point contact regime, two Andreev bound states carries supercurrent through the S-weak links-S interface. According to literature, current can be simply expressd Eq1) I_S=(1/Phi_0)*dE_A/d Phi here I_S : supercurrent, Phi_0 = flux quantum, E_A : Andreev bound...
  22. O

    What is the polarity of a Pn junction diode

    Hello all Textbooks teaches us that in the formation of Pn junction in between P and N type semiconductor a region is formed where free electrons of N diffused in P side and exhaust by the holes of P near the junction. Such a region becomes devoit of free charge careers and their are only ions...
  23. CKaiL

    PN Junction Q&A: Reverse Bias Voltage at Cathode

    Homework Statement [PLAIN]http:// Homework EquationsThe Attempt at a Solution It has becomes a P type semi conductor due to the fact that there is more acceptor than donor. From definition , forward bias is the direction of easy current flow while reverse bias is in the direction of little...
  24. 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...
  25. R

    Simulating Metal-Semiconductor Junction using SILVACO TCAD

    Hi, Sorry if it is too specific. I could not find a more specific group in the site. Would really appreciate if someone who has come across this already can find me a clue. I stumbled upon a strange result while playing with SILVACO TCAD, to simulate a metal semiconductor junction. I made a...
  26. 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?
  27. N

    Pn junction diode (series combo of voltage source and diode)

    The question is to solve the current through a resistor after a pn junction. (photo attached) As far as I'm aware the voltage source in the pn junction is (in this orientation) of opposite polarity to that of the 0.8V voltage source. From my understanding the answer goes like: V=IR I=V/R...
  28. 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...
  29. Z

    Questions about the "weak link" of Josephson junction

    1. It seems that in some Josephson junctions the insulator part is replaced by a gap, as is the so-called mesa. Is it true? 2. What does "weak link" exactly means? Somewhere it is said that the connection part is of a thickness of about 10 angstroms. What is the upper limit of the thickness...
  30. A

    Law of the PN junction under forward bias. Valid ?

    I'm currently studying the physics of the PN junction. I went though the derivation of the built-in potential in the PN junction under equilibrium: Diffusion current density = Drift current density D_{p}p\frac{dp}{dx} = EU_ppq where D_{p} : Diffusion coefficient for holes p = holes density...
  31. A

    Engineering Junction diode circuit problem

    Homework Statement (circuit attached) If the circuit shown, D2 has 10 times the junction area of D1. What value of V results? To obtain V=50mV, what current I2 is needed? Homework Equations I = I_S * (e^(V/V_T) - 1), V_T=25mV I(D2)/I(D1) = e^((VD2-VD1)/V_T) The Attempt at a Solution If D2 has...
  32. G

    Junction Capacitance in a GaAs Photodiode

    I am trying to get an estimation the junction capacitance of my GaAs Photodiode with respect to varying bias voltages. My Semiconductor Physics online textbook gives the following equations with ε0 = permittivity of free space εGgAs = GaAs dielectric constant μ = Mobility of...
  33. ranju

    What sets the clipping voltage in junction diode clipper circuits?

    In the given attachment there is a circuit given..and we have to find the output voltage waveform.. I have attached the options also..because according to me the " when input coltage is less than 5 V , it acts as open , most of the input voltage appears in output.. while when input voltage...
  34. Pythagorean

    Gap junction function in the nervous system

    In part branching off a discussion here, but also a discussion I've always been interested in having. I also want to take some time to answer the question in that thread: axo-axonic gap junctions in the hippocampus are thought to play a role in generating ultra-fast oscillations that have a...
  35. 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...
  36. 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...
  37. 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...
  38. L

    Josephson junction. Derivation.

    Homework Statement ## \alpha \frac{d^2\theta}{dt^2}+\beta\frac{d\theta}{dt}+V'(\theta)=V(t) ## Inertial effects are negligible at frequencies of up to several hundred megahertz, so the first therm can be neglected. I'm not sure if that means that ## \beta\frac{d\theta}{dt}+V'(\theta)=V(t) ##...
  39. 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?
  40. G

    PN Junction. Silicon vs Germanium

    When we connect P and N materials, electrons from N drift to P, thus create negative ions in P and positive ions in N. => electric field (barrier potential) must depend on an amount of electrons recombined with holes in P region. => The more electrons recombined, the more ions created, the...
  41. M

    Understand PN Junction Diode: Diffusion & Electrons

    If p-type semiconductor and n-type semiconductor of a diode are equally doped, and if the diode is forward biased, then holes will move toward the n-type semiconductor and electrons will move toward the p-type semiconductor and they will diffuse with each other and the ions become neutral atoms...
  42. M

    Understanding the Effect of Applied Magnetic Field on SQUIDs in Circuit QED

    Hello everyone, here is my problem I'm not sure where to start with this problem, I suppose if the phase difference due to the circulating current is negligible then the total phase difference can be written \Delta\phi_{tot}=\Delta\phi_{a}+\Delta\phi_{b}+ \Delta \phi_{B} In our notes we also...
  43. S

    Silicon Junction Diode: Charge Density and Potential Analysis

    Homework Statement In a silicon junction diode, the region of the planar junction between n-type and p-type semiconductors can be approximately represented as two adjoining slabs of charge, one negative and one positive. Away from the junction, outside these charge layers, the potential...
  44. 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...
  45. Saitama

    Capacitors - Finding the charges and potential at junction

    Homework Statement Three capacitors of 2μF, 3μF and 5μF are independently charged with batteries of emf's 5V, 20V and 10V respectively. After disconnecting from voltage sources, these capacitors are connected as shown in figure with their positive polarity connected to A and negative polarity...
  46. 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...
  47. 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...
  48. P

    How to find barrier potential of pn junction diode

    I want to know that when a pn junction diode is formed and barrier potential is setup then how can we determine the same theoretically. Also I wan to know that is there any relation between barrier potential and energy band gapSmall band gap small barrier? ?
  49. P

    Why is the Energy Level Higher on the P Side of a PN Junction Diode?

    Why energy level is higher on p side of pn junction diode as compare to n side of same
  50. 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...
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