Let apply bias and calculate current through the pn junction currents in pn junction from sze, 1981. Specifically, current will flow readily in one direction forward biased but not in the other reverse biased, creating the basic diode. The pn junction is the basis for diodes, certain transistors, solar cells, and other devices. Semiconductor pnjunction diodes physically, diodes are formed by the interface between two regions of oppositely doped semiconductor i. The line dividing the two regions, where n d n a 0, is the metallurgical junction. Shockley theory minority carrier concentrations at. Lecture 5lecture 5 pn junction diodes quantitative analysis math, math and more math georgia tech ece 4833 dr. Semiconductor pn junction diodes physically, diodes are formed by the interface between two regions of oppositely doped semiconductor i. The electrons come to the p region will combine with holes they. Here is some more theory for you to make sense of this which i wrote out of my own understanding. Ee lecture handouts pdf format download adobe acrobat to read pdf files. Thus, currents of ntype and ptype majority carriers flow toward the junction.
The region on the left is ptype with an acceptor density n a, while the region on the right is ntype with a donor density n d. May 15, 2018 we can create a pn junction by connecting face to face one ptype sand one ntype semiconductor crystal block by special techniques. The boltzmann approximation is to say that the resulting current being small compared with the components of this current, we consider that we are still in quasi equilibrium and therefore that the currents equation is still valid by replacing v. A pn junction is the metallurgical boundary between the n and pregions of a semiconductor crystal.
A pn junction consists of two semiconductor regions with opposite doping type as shown in figure 4. The diffusion forms a dipole charge layer at the pn junction interface. Junction field effect transistor jfet the single channel junction fieldeffect transistor jfet is probably the simplest transistor available. Similarly, electrons from nregion diffuse across the junction and recombine with the holes in pregion near the junction to form negative ions. Find out about the pn junction and its role in semiconductor electronics introduction. The pn junction is of great importance as it is the main control element for the semiconductor devices. A physical system where this constraint holds is a pn junction.
As the pn junction is formed, holes from pregion diffuse across the junction and recombine with the electrons in the nregion near the junction resulting in formation of positive ions in the nregion near the junction. How a pn junction formed in a diode engineering tutorial. Silicon a single silicon atom consists of fourteen negatively. A voltage v a pn junction 11 jan 2018 when semiconductor materials are doped, they become extrinsic semiconductors displaying di erent properties. The baseemitter junction is biased in the forward direction so only the intrinsic voltage drop across a pn junction appears. You can visualize a junction by taking a look at the adjacent diagram which is a very simple sketch showing such a junction. Actually, p n junction is fabricated by special technique, namely growing, alloying and diffusing methods.
Indian practical civil engineer handbook by pn khanna pdf this item. Chapter 4 pn junctions pn junction is present in perhaps every semiconductor device. Zero bias no external voltage potential is applied to the pn junction diode. Let us come to the point when a ptype semiconductor comes in contact with an ntype semiconductor, free electrons on ntype semiconductor nearer to the junction first migrate to the ptype semiconductor due to diffusion because the concentration of free electrons is much more in the ntype region than that of the ptype region. If less common germanium is used instead of silicon, the voltage drop is 0. Avalanche multiplication impact ionization of electronhole pairs tunneling through the junction zener breakdown at high doping concentrations, identical to that of tunneling in a metal semiconductor junction. The following treatment of bipolar junction behaviour assumes readers are familiar with basic semiconductor theory. This allows electrical current to pass through the junction only in. For integrated pn diodes, no special process steps available. The transfer of electrons from the n side of the junction to holes annihilated on the p side of the junction produces a barrier voltage. P n junction theory behind p n junction electrical4u.
Notice the depletion region penetrates more in the lighter doped material. You can check out and keep the portable breadboards, vb106 or vb108, from the 111lab for yourself only one each please this is the first of three labs on basic semiconductor components. Lecture 5lecture 5 pn junction diodes quantitative. The pn junction is a versatile element, which can be used as a. Pn junction one of the crucial keys to solid state electronics is the nature of the pn junction. Diode s a pn junction diode has a low impedance when the ptype layer is positively forward voltage biased with respect to the ntype layer.
C high input impedance, low power consumption, and a reversebiased pn junction are key characteristics of a field effect transistors. Alan doolittle n kt qv a i p p e and similarly at x x n n n x x a 1 2 1 2 kt qv d i n n e a n n p x x. The same is true of an ndoped semiconductor, but the junction between them can become depleted of charge carriers, and hence nonconductive, depending on the relative voltages of the two semiconductor regions. When carriers are injected across a forwardbiased junction, it emits incoherent light. The plane which divides these two parts is obviously known as the junction since these both types meet at this plane.
Coed school kolar road bhoapl department of physics project report investigatoryproject on pn junction and diodes project report submitted by govind patel submitted to mrs ratna hajela. If you are familiar with the theory of random walks, you. Semiconductors, diodes, transistors horst wahl, quarknet presentation, june 2001 electrical conductivity. Indian practical civil engineer handbook by pn khanna pdf. The passage of each carrier across the depletion region of the junction is a random. So that these can show properties of both depending upon the biasing of the circuit. Most of the commercial leds are realized using a highly doped n and a p junction. Forming a pn junction once in the ptype they can drop down into the valence band and to fill up one of the hole states. The recombination at the junction allows a battery current to flow through the pn junction diode. The theory of pn junctions in semiconductors and pn junction transistors.
A ptype material consists of silicon atoms and trivalent impurity atoms such as. The pn junction solidstate device theory electronics. Formation of pn junction in actual practice, a pn junction will not be formed if a ptype. This result into the formation of a charged depletion region formed at the pn junction. But when the device has no external applied forces, no current can flow. The electrode connecting to the ptype layer is called the anode, symbol a, and that connecting to the ntype layer.
The holes and electrons are carriers of electricity when they move about. Well as a 3rd year physics student i did a report on semiconductors. The pn junction is the fundamental building block of the electronic age. We have discussed semiconductors in detail with the energy band diagram if you want to read about its working, types and biasing you can go to our detailed semiconductor.
Doped semiconductors ntype materials ptype materials diodes and transistors. The most common method of making p n junction is called alloying. Pn junction diodes are a kind of basic diodes formed by using two types of extrinsic semiconductors i. Review of basic semiconductor and pn junction theory. Law of the junction o kt qv a i p p a e n n n n x x a 2 2 kt qv d i n n e a n n p x x law of the junction georgia tech ece 4833 dr. A voltage v a junction relative to the nside of the pn junction. Most semiconductor devices contains one or more pn junctions.
We can form a p n junction practically by doping one side of a semiconductor crystal by trivalent impurity and another side by pentavalent impurity. The passage of each carrier across the depletion region of the junction is a random event, and because of the energy barrier the carrier may travel in only one direction. Lecture 5lecture 5 pn junction diodes quantitative analysis. Pn junction underbiasing 14 boltzmanns approximation. Coed school kolar road bhoapl department of physics project report investigatoryproject on pn junction and diodes project report submitted by govind patel submitted to mrs ratna hajela registerationno. Lecture 16 the pn junction diode ii equivalent circuit model november 3, 2005 contents. Pn junctions consist of two semiconductor regions of opposite type. Pn junction capacitor under thermal equilibrium, the pn junction does not draw any much current but notice that a pn junction stores charge in the space charge region transition region since the device is storing charge, it s acting like a capacitor positive charge is stored in the nregion, and negative charge is in the pregion. Iv characteristics uwhenever an electron on the pside moves to the nside, it is replaced by an electron generated through one of the rg centers ohmic ohmic minority minority excess majority carriers alocal excess majority carriers alocal e e excess carriers move to the contact with a relaxation time. They are also called pn diodes in analogy with vacuum diodes. The following resource is associated with the next question.
Ee lecture notes university of california, berkeley. The result is that some of the free electrons from the donor impurity atoms begi. Sep 10, 2016 pn junction and zener diode 12 class project. This current reverse saturation current,i0 is given, according to the mann equation, by the formula k0 is a constant depending on the pn junction geometry and v0 is the built. In actual practice, the pn junction is not formed just by bringing a ptype semiconductor block near to an ntype semiconductor block. Kasap, 1990 2001 an ebooklet 1 pn junction the shockley model safa kasap department of electrical engineering university of saskatchewan canada although the hole and its negative counterpart, the excess electron, have been prominent in the theory of solids since the work of a. Indian practical civil engineers handbook by khanna p n reflects the efforts of p n khanna, who writes book related to the field of civil engineering. What is a pn junction when a ptype semiconductor is suitably joined to an ntype semiconductor, the contact surface is called pn junction. There is a builtin voltage at the pn junction interface that prevents penetration of electrons into the pside and holes into the nside. The area of the ptype near the junction becomes more negative due to the excess electrons while the ntype. Such junctions show a pronounced rectifying behavior. Pn junctions are fabricated from a monocrystalline piece of semiconductor with both a ptype and ntype region in proximity at a junction. When the ntype semiconductor and ptype semiconductor materials are first joined together a very large density gradient exists between both sides of the pn junction. Due to the abundance presence of holes or electrons, they become much better conductors than intrinsic semiconductors.
Valence band p n forming a pn junction electrons continue to diffuse across the junction. The pn junction possesses essential properties for modern electronics. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction. Formation of pn junction in actual practice, a pn junction will not be formed if. From the above, it follows that zero power dissipation occurs in an ideal diode. Jul 06, 2016 when you take a block of silicon and dope part of it with a trivalent impurity and the other part with a pentavalent impurity, a boundary called the pn junction is formed between the resulting ptype and ntype portions.