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. 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...
  2. A

    Solve Junction Diode Problem: V & I2 for D2=10xD1 Area

    Homework Statement If the circuit shown, D2= 10 times the junction area of D1. What value of V results? To obtain V=50mV, what current I2 is needed? Homework Equations i(D)=Is(eVD/VT-1)The Attempt at a Solution I know junction area is related to diode current, so D2 has 10 times current as...
  3. M

    Can PN Junction Charge Difference Be Utilized to Generate Electrical Energy?

    In a PN junction, if the P doped side becomes negatively charged with respect to the N doped side, does this mean that the application of an external metal wire, from the P side to the N side would cause current flow in that wire? Gien that the depletion region can be readily made at least...
  4. S

    Can a Thermocouple's cold junction can be electrically manipulated

    Can a Thermocouples cold junction can be electrically manipulated. Can a Thermocouples cold junction can be electrically mimicked to be a colder one; thus is it possible to make refrigerator out of thermocouples? electrons flow from hot to cold junction right ? can anyone give me link to more...
  5. B

    Josephson Junctions: Is There a Contradiction?

    Recently I am confused about this thing: according to the I-V curve, the resistance is 0 at zero bias, however, the conductance is finite by Andreev reflection? Is there a contradictory? Thanks!
  6. S

    Flow of gas in a t-junction with one junction sealed.

    Hi I'm running an experiment in the lab right now where the kit has a flow of gas (such as oxygen and nitrogen) from the side. The trouble is that I am trying to expose the gas to a powder which will throw itself everywhere. I am currently thinking of using a T-junction pipe (as in the image...
  7. H

    IV characteristic equation of triple junction solar cell

    Homework Statement The given quantities are the shunt resistances across each of the 3 diode junctions,assume them to be Rsh1,Rsh2,Rsh3; Tunnel diode resistances as Rt1 and Rt2, Photocurrent for each of the junction be Ip1,Ip2,Ip3 and bandgap of each subcell be Eg1,Eg2,Eg3 are given.Let V & I...
  8. 1

    Metal-Semiconductor-Metal Junction

    Hello everyone, Here i have metal-semiconductor-metal (M-S-M) junctions, p-type semiconductor separating two similar metals. In above picture semiconductor forming schottky barriers with metals, While in below picture these are ohmic contacts.. If assume that the semiconductor is very...
  9. P

    Heat Transfer: Heat from junction box to surface

    Homework Statement Calculate the surface temperature of a stainless steel junction box that is in a 35C ambient temperature environment. There are electrical "boxes" that generate 30W of heat inside of this box. Homework Equations (1) Q_dot_total = Q_dot_conv + Q_dot_rad (2) Q_dot_conv...
  10. A

    Drift current Is of PN junction under open-circuit conditions

    Hi, I need help to understand this section from my book. Here we are considering drift current Is of PN junction under open-circuit conditions. I don't understand why the drift current Is is indepentent of the value of the depletion layer voltage Vo. I think the voltage create an...
  11. M

    Space charge width pn junction

    Homework Statement Calculate the width of the space charge region in a pn junction when a reverse biased voltage is applied. Consider a silicon pn junction at T=300K with doping concentrations of Na=10^16 cm^-3 and Nd=10^15 cm-3. Assume that Ni=1.5*10^10 cm-3 and VR=5V Homework Equations...
  12. A

    Electric field inside PN junction in equilibrium

    I need help to understand this solution: Why electric field is zero at x < - b? I think it should be non-zero because the electric field from positive and negative ions don't completely cancel each other. How can you know E rises as x approaches zero?
  13. E

    Explaining the physical operation of semiconductor diode (pn junction)

    what is it ? please explaining the physical operation of semiconductor diode (pn junction).
  14. 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...
  15. C

    Why is Fermi Level constant across pn junction?

    I know this is true under thermal equilibrium, but I am not sure why. Why can't the Fermi level be a function of position relative to the pn-junction? How does that follow from thermodynamics/statistical mechanics?
  16. 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...
  17. W

    Relative velocity at a junction

    Homework Statement Two straight roads intersect at point O and cross at an angle Θ to one another, such that tan Θ = 3/4.Two cars, A and B are traveling towards O on these roads,A at 5 m/s and B at 8 m/s At a certain moment.A is 100 m from the junction and B, on the other road, is 200 m...
  18. I

    Depletion zone of a n-i junction

    Hi, I am interested in a junction between n doped and intrinsic GaAs, specifically the localization and width of the depletion zone (where the built-in E field is). In a p-n junction the depletion zone is calculated under the condition of electro-neutrality, if I see i-GaAs as really really low...
  19. D

    PN junction: basic electrostatics

    Hi, I'm stuck with the electrostatics of the PN junction. I just can't see why the electric field has to be negative in the depletion regio. The two equations give positive values for the Electric field in the intervals, so how can it be negative?? In the equation for the n regio, there are...
  20. N

    Estimate the number of electrons flowing in a semiconductor pn junction

    Homework Statement The drift current in a p-n junction is 20μA . Estimate the number of electrons crossing a cross section per second in the depletion region. Homework Equations Drift current is the current that occurs due to formation of holes and electrons in the depleted region from...
  21. 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?
  22. D

    Bipolar Junction Transistors - How does one read the datasheet?

    In particular, I am looking at a datasheet of a PNP BJT: http://www.fairchildsemi.com/ds/2N/2N3906.pdf I noticed that in the ON CHARACTERISTICS sub-heading, there were multiple h_{FE} values. I'm wondering how I could extract any meaningful information from that since the most common h_{FE}...
  23. E

    PN junction - advanced modeling

    Hello, let's start with a standard question: 1) A silicon diode has been characterized and as result we have a built-in potential of 0.53 V and a zero-bias capacitance of 1.3 mF/m^2. Assuming an abrupt junction (the measured grading coefficient is 0.5!) what are the respective doping levels...
  24. 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...
  25. T

    Israel's Formalism: The Metric Junction Method

    Hello guys , beside Einstein's General Theory of Relativity by hervik , is there any lecture or book about this case ? Thx
  26. M

    Metal-semiconductor junction with p-type and n-type and varying work functions

    Hi All, I am trying to get my head around the energy band diagrams associated with forming a metal-semiconductor junction for both p and n type s/c. I am also consider for each type, the case of \phim > \phin (work function of metal greater than work function on s/c) and \phim < \phin (work...
  27. 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...
  28. 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...
  29. 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...
  30. 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...
  31. E

    Specfic question about the formation of the depletion region in a pn junction

    Hi. I am reading about the pn junction, but I have a question. When the junction is formed the holes in the p-type material close to the junction diffuse across due to the concentration gradient. This leaves the acceptor atoms in the p-type material negatively charged. My question is: when...
  32. H

    Junction diode - unequally doped sides

    Why does the depletion layer penetrate a lightly doped side of a p-n junction diode?? Consider that there is a lightly doped p-side and a heavily doped n-side in a p-n junction diode , which is connected to a dc power supply in reversed biased. Now, I've read that depletion layer penetrates the...
  33. U

    PN junction diode barrier potential attracted to free electrons or holes?

    I am wondering about the barrier in PN junction diode.Due to diffusion negative ions are formed on the P side and Positive ions are formed on the N side of the diode.both opposite sides exert force of attraction and so a line of positive ions and negative ions align along the junction. The...
  34. O

    Conceptual short circuit diode / zero-bias base collector junction BJT question

    Why exactly is there zero current flowing through a diode when it is short circuited, given the presence of the barrier potential? My current understanding is that the drift current precisely balances the diffusion current. But if you take a diode and short it with a wire, wouldn't you then also...
  35. 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...
  36. 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...
  37. 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...
  38. D

    Why Can't the Voltage at a PN Junction be Measured from the Outside?

    I am having a hard time to find answers to 2 simple questions regarding semiconductors. Firts, at a PN junction diffusion creates a potential step. Why can this voltage not been measured from the outside. The schoolbook answer is, that there are diffusion potential at the wire connections...
  39. F

    Pn junction, diode and energy level of conduction band during forward biasing

    Hello Forum, I am looking at the energy levels between the n and p regions of a diode. The p-side has a conduction band that starts at a higher energy (same for the valence band). The n-side has the valence and condution bands that are at lower energy. The Fermi energy line is the same...
  40. K

    The correct movement of charge in PN junction

    Homework Statement I've been reading and I just want to make sure that this is the correct way which pv cells work, I feel this is not correct. I want to find where I am wrong. Once the p and n doped semiconductors are put together some carriers migrate and combine to form a depletion zone...
  41. 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...
  42. F

    Back gating of Metal/Semiconductor junction

    When a metal is brought into contact with a semiconductor (n-type) a depletion layer is formed at the metal-semiconductor interface on which band bending occurs. In the full-depletion model it is assumed that all donors are positively charged (withi this layer). What happens if a back-gate (with...
  43. Pythagorean

    Gap junction modulators for C. elegans

    Are there any known gap junction openers/closers for C. elegans? I've googled far and wide for weeks. Trimethylamine, quinine, and carbenoxolone are known to work with connexins in mammals. They also happen to be expensive and require more paperwork, so I don't want to go through the steps...
  44. C

    Forward Biased PN Junction Help: Silicon Band Diagram & Capacitance Calculation

    Homework Statement Assume silicon, at room temperature (300k) and complete ionization. An abrupt n+-p junction with Nd=10^20 cm^-3 and Na=10^17 cm^-3 is forward biased at 0.5V Homework Equations a)Draw the band diagram, label n and p regions, show direction of the current flow. Also what is...
  45. F

    Depletion Layers in pn junction

    Hi, Can someone please tell me if it is true that in heavily doped pn junctions, the electric field that prevents further diffusion of holes and electrons is set up more quickly than in less heavily doped pn junctions? Is this essentially because the holes and electrons recombine more...
  46. M

    Calculating i5 Using Kirchoff's Junction Rule

    Homework Statement Calculate the current i5 in the configuration. Use the following data: i1=8.65 A, i2=5 A, i3=7.85 A, and i4=8.5 A. Homework Equations Kirchoff's junction rule states that the sum of the currents meeting at a junction has to equal zero. The Attempt at a Solution...
  47. B

    What Happens When PN Junction is Shorted?

    Hi friends, here's my question. The two terminals of a PN junction are at different potentials so, if I connect a them with a wire i.e. short them, What would happen? Would the potential difference between the two ends becomes zero or what? As far I'm understanding, there would be a flow of...
  48. 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...
  49. R

    Using Kirchoff's junction rule for current from a battery.

    Homework Statement Use Kirchhoff's junction rule to calculate the current supplied by the battery. Homework Equations attached a pic. The Attempt at a Solution Where do we start?
  50. S

    Temperature at a junction between two rods?

    Homework Statement A girl needs a rod that will carry heat from a pan of boiling water to a mixture of ice and water so that the ice will melt more quickly. She has a copper rod of diameter DCu and an aluminum rod of diameter DAl, neither of which is long enough to reach from the pan to the...
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