A pn junction is the metallurgical boundary between the n and pregions of a semiconductor crystal. 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. Physics of semiconductor devices pn junction depletion width problem a silicon pn diode has a doping of n d 81015 1 cm3 and n a 210 16 1 cm3. Depletion layer and diffusion capacitance contributions article pdf available in european journal of physics 142. Current flow is proportional to evavref due to the exponential decay of carriers into. It acts as an open circuit when it is reversed biased, i. Physics of pn junctions and semiconductor devices springerlink. The result is that some of the free electrons from the donor impurity atoms begin to migrate across this newly formed junction to fill up the holes in the ptype. Try one of the apps below to open or edit this item. Semiconductors, diodes, transistors horst wahl, quarknet presentation, june 2001 electrical conductivity. Pdf version introduction to quantumatk atk reference manual.
If an external potential is applied to the terminals of pn junction, it will alter the potential between the p and n regions. An arrangement consisting a p type semiconductor brought into a close contact with ntype semiconductor, is called a p n junction. Finally, from device physics and i would love to teach. If the silicon crys tal is very pure, then the outer four electrons occupy all of the covalent. Current flow is constant due to thermally generated carriers swept out by efields in the depletion region forward bias. When a pn junction is used as a detector of charged particles or of photons. Pdf physics of imaging pn junctions by scanning tunneling. The pn junction is the fundamental building block of the electronic age. What are the depletion width in the nregion, the depletion width in the pregion, and the builtin potential at 300k.
If an external potential is applied to the terminals of pn junction, it will alter the potential between the p and nregions. The p n junction is a versatile element, which can be used as a. The term band gap refers to the energy difference between the top of the valence outer electron band and the bottom of the conduction free. To plot voltampere characteristics of silicon pn junction diode. As the base is thin and lightly doped, then it will not work as a pn junction. Semiconductor physics semiconductors and diodessemiconductors. The diffusion of electrons and holes into the depletion layer decreases its width. In a semiconductor, the p n junction is created by the method of doping. Pn junctions consist of two semiconductor regions of opposite type. Since the ntype region has a high electron concentration and the ptype a high hole concentration, electrons diffuse from the ntype side to the ptype side. P n diode has excessive holes in one side of the junction and excess free electrones on the other but both sides are electrically neutral.
Pn junction diode and characteristics of pn junction diode. If the junction is forward biased by applying a positive voltage v. A solar cell, or photovoltaic cell, is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. Device physics i pn junctions junction capacitance martin p. This allows electrical current to pass through the junction only in. Working of pn junction diode with biasing, characteristics. If we join a piece of p type material to a pieceof n type material such that the crystalstructure remains continuous at the boundary, a pn junction is formed 2. Pn junctions are formed by joining ntype and ptype semiconductor materials, as shown below. Pn junction forward bias positive voltage placed on ptype material holes in ptype move away from positive terminal. Pn diode has excessive holes in one side of the junction and excess free electrones on the other but both sides are electrically neutral. Forward bias current flows reverse bias no current flow. In order to find an upper theoretical limit for the efficiency of p. The term pn junction refers to the joint interface and the immediate surrounding area of the two semiconductors. Pn junction iv characteristics putting it all together reverse bias.
Electron current density is a combination of drift and diffusion currents, which must. The biased pn junction an externally applied potential will alter the potential difference between the pand nregions. This potential difference can alter the flow of majority carriers, so that the pn junction can be used as an opportunity for the diffusion of electrons and holes. Silicon a single silicon atom consists of fourteen negatively. Pn junction physics from ece 340 at california state university, northridge. N and p type regions form the cathode and anode respectively operation prior to voltage being applied to the diode, at the junction of the ptype and ntype regions, free electrons from the ntype side move to the ptype side and.
P n junctions consist of two semiconductor regions of opposite type. Writing a book on semiconductor device physics and design is never complete and probably never completely satisfying. Electric field distribution in a reversebiased pn junction 1 problem. This essentially annihilates them both leaving region at the junction depleted of any charge. Pn junction under reverse bias p connected to negative terminal of battery, n connected to positive terminal at n, electrons move towards the positive terminal, creating a larger area of positive charges. Class12 section contents certificate acknowledgement introduction applications summary bibliography certificate this is to certify that this project has been made by of class xii on zener diode under the guidance of our physics teacher ms and has been completed successfully. Jan 29, 2019 the diffusion voltage across a pn junction diode can be expressed as.
Starting from the structure of matter and various types of bonds in the first chapter the mechanical properties are treated in the second chapter. Higher physics second in a series of 3 videos on semiconductors. P type and n type semiconductors, takenseparately are of very limited use. The p n junction is the fundamental building block of the electronic age. A pn junction is formed when two types of semiconductors, n type excess electrons and p type excess holes, come into contact.
It is because that electrons are majority carrier in n p n transistor while holes are majority carrier in p n p transistor. Initially the chemical potential is different in the two sides, but thermal equilibrium requires that the chemical potential be uniform. These two emerging industries based on pn junctions make a significant contribution to the reduction in fossil fuel consumption. This potential difference can alter the flow of majority carriers, so that the pn junction can be used as an opportunity for the diffusion of. The pside or the positive side of the semiconductor has an excess of holes and the nside or the negative side has an excess of electrons. P n junction also known as a diode one of the basics of semiconductor technology created by placing n type and p type material in close contact diffusion mobile charges holes in p type combine with mobile charges electrons in n type. This in turn will modify the flow of majority carriers, so that the junction can be used as a gate. Physics of semiconductor devices p n junction depletion width problem a silicon p n diode has a doping of n d 81015 1 cm3 and n a 210 16 1 cm3. In the p type region there are holes from the acceptor impurities and in the n type region there are extra electrons when a p n junction is formed, some of the electrons from the n region which have reached the conduction band are free to diffuse across the junction and combine with holes. You will define the structure of a hpassivated inas slab along the 100 direction, and set up a pin junction. This video covers the formation of the p n junction and how it performs when forward and reverse biased. This book covers the two most important applications of semiconductor diodes solar cells and leds together with quantitative coverage of. A pn junction diode is a twoterminal electronics element, which can be classified as either step graded or linear graded.
That means diffusion potential prevents charge carriers to cross the junction. Initially they diffuse to create an equilibrium of numbers of electron and hole, but in this way they create electric potential on the opposite side off the flow. Dependence of fermi level with doping concentration e i. Approximate solution using the full depletion approximation a abrupt pn junction an easy way to derive the depletion layer widths in a pn diode is to treat it as a combination of two schottky diodes, one with an ntype semiconductor and an other with a ptype. The diffusion potential creates a potential barrier for further migration of free electrons from n type side to p type side and holes from p type side to n type side. When ptype and ntype materials are placed in contact with each other, the junction behaves very differently than either type of material alone. A pn junction diode is formed when a p type semiconductor is fused to an n type semiconductor creating a potential barrier voltage across the diode junction the effect described in the previous tutorial is achieved without any external voltage being applied to the actual pn junction resulting in the junction being in a state of equilibrium. Adapted from semiconductor device physics and design umesh mishra and. Formation of p n junction forward bias reverse bias p n. As the base is thin and lightly doped, then it will not work as a p n junction. They are also called p n diodes in analogy with vacuum diodes.
Alan doolittle 2 2 ln ln ln i a d bi a i d p n bi n n n q kt v n n n q kt n x n x q kt v movement of electrons and holes when forming the junction for nand1015cm3 in silicon at room temperature. 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. During forward biasing, holes move towards n side and electrons move towards p side. A light emitting diode led is essentially a pn junction diode. The charge in the depletion region per cross sectional area is the depletion width times the concentration of ionic charge qn. Semiconductor diode project free download as powerpoint presentation. In this type of diode, we dope one side of a semiconductor piece with an acceptor impurity and another side with a donor impurity. Physics of semiconductor devices pn junction depletion. Semiconductor physics the pn junction biasing the pn junction the diode trouble shooting.
V bi k b t ln p p n, 124 or p p n e ev bi k b t n n p, 125 where the last step is based on the fact that at equilibrium n p p n n n. It is a form of photoelectric cell, defined as a device whose electrical characteristics, such as current, voltage, or resistance, vary when exposed to light individual solar cell devices can be. They are also called pn diodes in analogy with vacuum diodes. Pn junction diode is one of the fundamental elements in electronics. Electron energy band fermi level electrostatics of. Depletion layer the region in the middle of a pn diode junction that is almost void of charge carrying. When carriers are injected across a forwardbiased junction, it emits incoherent light.
Band diagram of pn junction under a equilibrium and b forward. The purpose of this tutorial is to show how to set up and perform calculations for a device based on an inas slab. A pnjunction diode is formed when a ptype semiconductor is fused to an ntype semiconductor creating a potential barrier voltage across the diode junction the effect described in the previous tutorial is achieved without any external voltage being applied to the actual pn junction resulting in the junction being in a state of equilibrium. Pn junction region of charges left behind dopants fixed in crystal lattice. Doped semiconductors ntype materials ptype materials diodes and transistors.
Pn junction physics ece340 electronics i pn junction. Imax and imelt specify the pn junction explosion current. The pn junction is a versatile element, which can be used as a. In other words, minority carrier injection happens on both pside in a normal diode without bias electrons are a minority on pside and nside holes are a minority on nside of the diode. Full practical pn junction diode with readings, download pdf. Imax and imelt can be specified in the device model or in the options component.
Pn junction also known as a diode one of the basics of semiconductor technology created by placing ntype and p type material in close contact diffusion mobile charges holes in ptype combine with mobile charges electrons in ntype. Because of its electrical properties, silicon is called a semiconductor. Similarly, holes flow by diffusion from the ptype side to the ntype side. A pn junction is a boundary or interface between two types of semiconductor materials, ptype and ntype, inside a single crystal of semiconductor. Most of the commercial leds are realized using a highly doped n and a p junction. Pn diode junction when a p and an n type semiconductor are joined together they form a single semiconductor which allows current to only flow in 1 direction.
This is a book which covers the topic of solid state physics comprehensively. A pn junction is created in silicon by a doping process. What are the depletion width in the n region, the depletion width in the p region, and the builtin potential at 300k. If the imelt value is less than the imax value, the imelt value is increased to the imax value. Pn junction one of the crucial keys to solid state electronics is the nature of the pn junction. Such junctions show a pronounced rectifying behavior. Initially the chemical potential is different in the two sides, but thermal equilibrium requires that the chemical potential be.
By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the p n junction. Imax and imelt specify the p n junction explosion current. The process of doping is explained in further details in the next section. Charge density in an abrupt pn junction physics forums. If more holes and electrons will diffuse, wouldnt they form more immobile ions i. Apr 02, 2018 higher physics second in a series of 3 videos on semiconductors. At p, holes move towards the negative terminal, creating a large area of negative charges. This video covers the formation of the pn junction and how it performs when forward and reverse biased. Pn junction theory for semiconductor diodes electronicstutorials. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction. The p side or the positive side of the semiconductor has an excess of holes and the n side or the negative side has an excess of electrons.
A p n junction is the metallurgical boundary between the n and p regions of a semiconductor crystal. How current flow takes place in a pn junction diode. Specifically, current will flow readily in one direction forward biased but not in the other reverse biased, creating the basic diode. This book covers the two most important applications of semiconductor diodes solar cells and leds together with quantitative coverage of the physics of the p n junction. Physics of semiconductor devices pn junction depletion width. Dec 31, 2015 p n junction under reverse bias p connected to negative terminal of battery, n connected to positive terminal at n, electrons move towards the positive terminal, creating a larger area of positive charges. It is because that electrons are majority carrier in np n.
Aug 11, 2011 these two emerging industries based on p n junctions make a significant contribution to the reduction in fossil fuel consumption. Electron energy band fermi level electrostatics of device. A pn junction is an interface or a boundary between two semiconductor material types, namely the ptype and the ntype, inside a semiconductor. The second chapter also includes a discussion of hookes law, plastic flow, dislocations, elasticity etc. The difference between an insulator and a semiconductor lies in the size of the band gap.
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