Zero bias no external voltage is applied to the pn junction diode. May 16, 2015 for the love of physics walter lewin may 16, 2011 duration. Although it is not discussed majorly outside the concept of pn junction diode and sometimes the transistor, a pn junction is an essential topic in semiconductor electronics. This is the basic construction of the pn junction diode. The electrons come to the p region will combine with holes they. The standard equation for current through a diode is. A pn junction is formed when an ntype material is fused together with a ptype material creating a semiconductor diode. Pn junction diodes quantitative analysis math, math and more math georgia tech ece 4833. The semiideal diode had a leakage current across the junction the reverse saturation current, shown by i. The diode conducts when forward bias is applied and it will introduce zero resistance in the circuit. The valence band and conduction band in ntype material are slightly lower than that of ptype material. It has a particular voltage known as break down voltage, at which the diode break downs while reverse biased. Normally the voltage is taken along the xaxis and current along yaxis.
Image source forward biasing a pn junction diode is very simple. In the case of normal diodes the diode damages at the break down voltage. Zener diode is a pn junction diode specially designed to operate in the reverse biased mode. The pnjunction is the root for semiconductor diodes. This causes the holes to move toward the depletion region and the free electrons to move toward the depletion region. I o is the saturation current, so called because at sufficiently large reverse bias v 3kt, say i.
So, in this pn junction tutorial, we will discuss some of the basics of a pn junction, how a pn junction is formed, characteristics of pn junction and many other aspects. 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. The ohms law said that the voltage applies across the diode is equal to the product of the current and resistance applied across the diodes. As shown in the figure, pn junction diode is a 2 terminal polarity sensitive device. You just need to take a battery whose values can be varied from o to v volts, connect its positive terminal to the pside of pn junction diode and then connect the negative terminal of battery to the nside of the pn junction diode. The symbolic representation of the diode is as follows. Unilluminated pn junction diode photon energy spectrum. Lecture 5lecture 5 pn junction diodes quantitative. Connect currents across scl to get total junction current, i d features and limitations of the model engineering the minority carrier injection across a junction deviations at low and high current levels deviations at large reverse bias 6. This allows electrical current to pass through the junction only in. A pn junction with open terminals excluding minority carriers f.
Such junctions show a pronounced rectifying behavior. Qualitative treatment of pn junction if we return to consider the energy level diagram we can regard the potential difference, v o, as a barrier to the flow of majority carriers. When the diode is forwardbiased, it can be used in led lighting applications. 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. A pn junction diode is a twoterminal electronics element, which can be classified as either step graded or linear graded. A pn junction is a boundary or interface between two types of semiconductor materials, ptype and ntype, inside a single crystal of semiconductor. Smith department of eecs university of california, berkeley eecs 105 spring 2004, lecture 19 prof. The pn junction biasing the pn junction the diode trouble shooting. Silicon a single silicon atom consists of fourteen negatively. A semiconductor diode is a two terminal electronic component with a pn junction. The pn junction is the fundamental building block of the electronic age.
Draw the energy level diagram of a pn junction and explain how a junction barrier is developed across an unbiased junction. This pn diode applications are very useful for beginners. View notes pnjunction iv characteristics from eie 577 at hong kong polytechnic university. Lecture 5lecture 5 pn junction diodes quantitative analysis. 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. We can then fill in the junction region of the band diagram as. A pn junction is the metallurgical boundary between the n and pregions of a semiconductor crystal. 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. Simplified physical structure construction on a cmos chip. The depletion region shrinks allowing current to flow. Diode theory diode as a conductor when a voltage is applied current will flow. P n junction theory behind p n junction electrical4u. The pn junction diode is the basic semiconductor diode format. A pnjunction is formed when an ntype material is fused together with a ptype material creating a semiconductor diode.
In the previous tutorial we saw how to make an ntype semiconductor material by doping a silicon atom with small amounts of antimony and also how to make a ptype semiconductor material by doping another silicon atom with boron. The anode which is the positive terminal of a diode is represented with a and the cathode. P type and n type semiconductors, takenseparately are of very limited use. Vi characteristics of pn junction diode electronics post. Pn junction tutorial introduction to pn junction diodes. Rectification is an application of the pn junction diode. Semiconductor, silicon, pn junction, forward bias, reverse bias, diode. The pnjunction diode is mainly used for rectification purpose, whereas the zener diode is used for providing the. I is the current through the diode i s is the reverse saturation current v is the voltage across the diode can be positive or negative n is a junction constant typically around 2 for diodes, 1 for transistors. A half wave rectifier is a device which makes use of key properties of a pn junction diode. Since a junction forms between a p type and n type material it is called as pn junction.
Also, it explains the phenomenon of shockleyqueisser limit. A pn junction diode is a twoterminal electronics element, which can be classified as either. The pnjunction obey the ohms law whereas zener diode does not obey the ohms law. Half wave rectifier circuit with diagram learn operation. The arrow indicates the flow of current through it when the diode is in forward biased mode, the dash or the block at the tip of the arrow indicates the blockage of current from the opposite direction. Now, if we join the two types of semiconductors ptype and ntype together then a new device is formed called as pn junction diode. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction. The result is that some of the free electrons from the donor impurity atoms begi. 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. So to understand the underlying theory behind a half wave rectifier, you need to understand the pn junction and the characteristics of the pn junction diode. Najmabadi, ece65, winter 2012 high concentration of h on the p side holes diffuse towards the junction high concentration of e on the n side electrons diffuse towards the junction n side is positively charged because it has lost electrons. Junction transistor, transistor current components, transistor as an amplifier, c b and c e configurations. Junction transistor, transistor current components, transistor as an amplifier, c b and c e. It is the most essential and the basic building block of the electronic device.
Working of pn junction diode if an external potential is applied to the terminals of pn junction, it will alter the potential between the p and nregions. In this video, the pn junction diode has been explained. The word diode can be explained as di means two and ode is obtained from electrode. This diode may represent effects such as depletion region recombination n2, or tunneling. Vi characteristics of pn junction diode in 3biasing modes.
Iv characteristics pn junction diode reverse biasing a pn junction when the polarity of the battery is reversed, the cathode is connected to positive end of the battery and anode to negative. From the above, it follows that zero power dissipation occurs in an ideal diode. For the love of physics walter lewin may 16, 2011 duration. 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. Jan 29, 2019 pn junction diode is one of the fundamental elements in electronics.
Apr 29, 2020 quantitative theory of pn junction diode electrical engineering ee notes edurev is made by best teachers of electrical engineering ee. The diode is firmed by doping a semiconductor like silicon or germanium with trivalent impurity e. We have seen how a diode is made with p and n semiconductors but. A circuit with input resistance ri uses a zener diode with breakdown voltage vbr 5v to protect itself from large input voltages. Voltampere vi characteristics of a pn junction or semiconductor diode is the curve between voltage across the junction and the current through the circuit.
Semiconductor pn junction diodes physically, diodes are formed by the interface between two regions of oppositely doped semiconductor i. It is a type of switch which only allows the forward current to pass through it. Review, pn junctions, fermi levels, forward bias prof j. From single attomsto solid crystals isolated li atom conducting metal has welldefined, isolated allowable electron energy. A pn junction 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 diode baising and its vi characteristics. This causes electrons from nregion to get attracted to positive terminal of the battery and holes by the negative terminal. In this type of diode, we dope one side of a semiconductor piece with an acceptor impurity and another side with a donor impurity. 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. A pn junction diode is formed by doping one side of a piece of silicon with a ptype dopant boran and the other side with a ntype dopant phosphorus. There is also a difference in the reverse bias region due to both material characteristics and fabrication of the diode junction. Dec 21, 2018 in this video, the pn junction diode has been explained. After having known about various components, let us focus on another important component in the field of electronics, known as a diode. And based on the applied voltage, there are three possible biasing conditions for the pn junction diode, which are as follows.
Working of pn junction diode with biasing, characteristics. I o1 is a perfect diode with ideality factor, n 1 and a leakage current i o1 i o2 is a nonperfect diode with ideality factor, n 1 and a leakage current i o2. Pn junctions consist of two semiconductor regions of opposite type. Vref from our previous qualitative analysis equation is the thermal voltage, ktq. And the working of this pn junction diode under forward and reverse bias has been explained.
Semiconductor physics semiconductors and diodessemiconductors. The equivalent circuit of the zener diode in the reversebias. The pn junction diode is used for rectification purpose because it allows the current to flow only in one direction. Pn junction diode and characteristics of pn junction diode.
Quantitative theory of pn junction diode electrical. It is acting as normal diode while forward biasing. Pn junction diode applications pn diode applications. The pn junction diode is a twoterminal device, which is formed when one side of the pn junction diode is made with ptype and doped with the ntype material.
It is used for many forms of rectification for current levels both large and small, as well as high and low voltage levels, and it finds many uses in all manner of electronic circuits. Theory a semiconductor pn junction diode is a two terminal electronic device that allows current in only one direction. Forward bias current flows reverse bias no current flow. The pn junction has the very useful property that electrons are only able to flow in one direction. On the other hand, the zener diode allows both the forward and reverse current to pass through it. This lecture uncovers the basic science of semiconductor devices and solar cells, including pn junction and photovoltaic effects. Ivcharacteristics semiconductoroptoelectronics 1 qualitative derivation. I o we can recast the expression for i o in terms of doping densities by noting that n p n i 2n a andp n n i 2n d. This page of application notes section covers pn junction diode applications. The shift of electrons from n side of the pn junction to holes annihilated on the p side of the pn junction produces a potential barrier voltage. Najmabadi, ece65, winter 2012 high concentration of h on the p side holes diffuse towards the junction high concentration of. This document is highly rated by electrical engineering ee students and has been viewed 1949 times. 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.
189 1602 250 710 438 1617 1231 1261 338 1506 808 1074 709 1165 758 1189 1501 913 426 608 1089 1032 498 602 375 1331 1186 997 902 804 585 1034