The theory of pn junctions in semiconductors and pn junction transistors. 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. Jan 21, 2019 what is a pn junction when a ptype semiconductor is suitably joined to an ntype semiconductor, the contact surface is called pn junction. Actually, p n junction is fabricated by special technique, namely growing, alloying and diffusing methods. What is a pn junction when a ptype semiconductor is suitably joined to an ntype semiconductor, the contact surface is called pn junction. Lecture 16 the pn junction diode ii equivalent circuit model november 3, 2005 contents. Junction field effect transistor jfet the single channel junction fieldeffect transistor jfet is probably the simplest transistor available. 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. This result into the formation of a charged depletion region formed at the pn junction. For integrated pn diodes, no special process steps available.
When carriers are injected across a forwardbiased junction, it emits incoherent light. A voltage v a pn junction 11 jan 2018 when semiconductor materials are doped, they become extrinsic semiconductors displaying di erent properties. Sep 10, 2016 pn junction and zener diode 12 class project. A physical system where this constraint holds is a pn junction. A pn junction is a boundary or interface between two types of semiconductor materials, ptype and ntype, inside a single crystal of semiconductor. 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 pn junction is the basis for diodes, certain transistors, solar cells, and other devices. Such junctions show a pronounced rectifying behavior. Notice the depletion region penetrates more in the lighter doped material.
A pn junction consists of two semiconductor regions with opposite doping type as shown in figure 4. Similarly, electrons from nregion diffuse across the junction and recombine with the holes in pregion near the junction to form negative ions. Formation of pn junction in actual practice, a pn junction will not be formed if. The following treatment of bipolar junction behaviour assumes readers are familiar with basic semiconductor theory. 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. You can visualize a junction by taking a look at the adjacent diagram which is a very simple sketch showing such a junction. Silicon a single silicon atom consists of fourteen negatively. 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. The plane which divides these two parts is obviously known as the junction since these both types meet at this plane. Thus, currents of ntype and ptype majority carriers flow toward the junction.
Let apply bias and calculate current through the pn junction currents in pn junction from sze, 1981. Semiconductor pnjunction diodes physically, diodes are formed by the interface between two regions of oppositely doped semiconductor i. Find out about the pn junction and its role in semiconductor electronics introduction. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn 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 pn junction is of great importance as it is the main control element for the semiconductor devices. 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. Shockley theory minority carrier concentrations at. 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. The electrons come to the p region will combine with holes they. 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. Doped semiconductors ntype materials ptype materials diodes and transistors.
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. A pn junction is the metallurgical boundary between the n and pregions of a semiconductor crystal. 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. The line dividing the two regions, where n d n a 0, is the metallurgical junction. Characteristics of the diode in reverse biased mode, the current flowed in the diode is extremely small. 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.
Indian practical civil engineer handbook by pn khanna pdf this item. The holes and electrons are carriers of electricity when they move about. If less common germanium is used instead of silicon, the voltage drop is 0. From the above, it follows that zero power dissipation occurs in an ideal diode. When ptype and ntype materials are placed in contact with each other, the junction behaves very differently than either type of material alone. The pn junction possesses essential properties for modern electronics. Zero bias no external voltage potential is applied to the pn junction diode. 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. Indian practical civil engineer handbook by pn khanna pdf. They are also called pn diodes in analogy with vacuum diodes.
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. 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. Pn junction one of the crucial keys to solid state electronics is the nature of the pn junction. Lecture 5lecture 5 pn junction diodes quantitative analysis math, math and more math georgia tech ece 4833 dr. 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. A voltage v a junction relative to the nside of the pn junction. Lecture 5lecture 5 pn junction diodes quantitative. A light emitting diode led is essentially a pn junction diode.
Pn junction underbiasing 14 boltzmanns approximation. The pn junction is a versatile element, which can be used as a. Pn junction diodes are a kind of basic diodes formed by using two types of extrinsic semiconductors i. Lecture 5lecture 5 pn junction diodes quantitative analysis. How a pn junction formed in a diode engineering tutorial. The default pnjunction device geometry we use in our analyses, including two alternative coordinate systems for convenience. Well as a 3rd year physics student i did a report on semiconductors. The following resource is associated with the next question. 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. Most of the commercial leds are realized using a highly doped n and a p junction. P n junction theory behind p n junction electrical4u. Ee lecture notes university of california, berkeley. In actual practice, the pn junction is not formed just by bringing a ptype semiconductor block near to an ntype semiconductor block. The pn junction is the fundamental building block of the electronic age.
The recombination at the junction allows a battery current to flow through the pn junction diode. C high input impedance, low power consumption, and a reversebiased pn junction are key characteristics of a field effect transistors. The area of the ptype near the junction becomes more negative due to the excess electrons while the ntype. The baseemitter junction is biased in the forward direction so only the intrinsic voltage drop across a pn junction appears. 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. Here is some more theory for you to make sense of this which i wrote out of my own understanding. Pn junctions are fabricated from a monocrystalline piece of semiconductor with both a ptype and ntype region in proximity at a junction. 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. Due to the abundance presence of holes or electrons, they become much better conductors than intrinsic semiconductors.
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. A ptype material consists of silicon atoms and trivalent impurity atoms such as. Pn junctions consist of two semiconductor regions of opposite type. Formation of pn junction in actual practice, a pn junction will not be formed if a ptype. The diffusion forms a dipole charge layer at the pn junction interface. The result is that some of the free electrons from the donor impurity atoms begi. Ee lecture handouts pdf format download adobe acrobat to read pdf files. 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. Semiconductor pn junction diodes physically, diodes are formed by the interface between two regions of oppositely doped semiconductor i. Review of basic semiconductor and pn junction theory. The most common method of making p n junction is called alloying. 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 passage of each carrier across the depletion region of the junction is a random. 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 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. Semiconductors, diodes, transistors horst wahl, quarknet presentation, june 2001 electrical conductivity.
This allows electrical current to pass through the junction only in. If you are familiar with the theory of random walks, you. 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. 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 bi by v. Chapter 4 pn junctions pn junction is present in perhaps every semiconductor device. The electrode connecting to the ptype layer is called the anode, symbol a, and that connecting to the ntype layer. The pn junction solidstate device theory electronics. Specifically, current will flow readily in one direction forward biased but not in the other reverse biased, creating the basic diode. There is a builtin voltage at the pn junction interface that prevents penetration of electrons into the pside and holes into the nside. But when the device has no external applied forces, no current can flow. So that these can show properties of both depending upon the biasing of the circuit. Valence band p n forming a pn junction electrons continue to diffuse across the junction. 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.