Pn junctions are formed by joining ntype and ptype semiconductor materials, as shown below. The word diode can be explained as di means two and ode is obtained from electrode. Such junctions show a pronounced rectifying behavior. Due to the cancellation of electrons and holes at the junction, the junction will have no. 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. A pn junction is formed by diffusing a ptype material to an ntype wafer and there are several other ways as well, see your text. This is the voltage required to reach a flat band diagram and sets an upper limit typically an overestimate for the voltage that can be applied to a diode before it burns itself up. Semiconductor, silicon, pn junction, forward bias, reverse bias, diode. Lecture 15 the pn junction diode i mit opencourseware. Ece 255, pn junction and diode 16 january 2018 in this lecture we would continue with the discussion of the pnjunction which is important for the understanding of the working of a diode. Free electrons in the n region near the pn junction begin to diffuse across the junction and fall into holes near the junction in the p region. The increase in resistance of the pn junction results in the junction behaving as an insulator. From the above, it follows that zero power dissipation occurs in an ideal diode. The diode conducts when forward bias is applied and it will introduce zero resistance in the circuit.
The doping profile is our starting point to analyze pn junction electrostatics, since it combines the information given for n d and n a. Diode allows current to pass in only one direction. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction. This is a physics video for grade 1112 students about pn junction diode, its properties, characteristics and uses. At the instant of the pn junction formation, the free electrons near the junction in the n region begin to diffuse across the junction into the p region where they combine with holes near the junction, as shown in figure b. We prefer to read our article on pn junction first before reading this guide for maximum. The animation below shows the formation of the e at the junction between n and ptype material. Understanding the formation and functioning of a pn junction is paramount to analyzing the working of semiconductor devices. In this type of diode, we dope one side of a semiconductor piece with an acceptor impurity and another side with a donor impurity. In this tutorial, we will learn about pn junction diodes and in particular the characteristics and working of pn junction diode. This understanding will lay a better foundation for exploring further into different aspects of semiconductor electronics. Energyband diagram of pn junction in thermal equilibrium in which both the n and p region are degenerately doped. However, unlike a resistor, a diode does not behave linearly with respect to the applied voltage as the diode has an exponential currentvoltage iv relationship.
A diode is a 2 lead semiconductor that acts as a one way gate to electron flow. The term junction refers to the boundary interface where the two regions of the semiconductor meet. A pn junction diode is one of the simplest semiconductor devices around, and which has the characteristic of passing current in only one direction only. We have also learned about diffusion current, depletion region. Pn junction diode and characteristics of pn junction diode. It will help you to grasp concepts behind pn junction even better. Pdf barrier potential across semiconductor pn junction and. Silicon a single silicon atom consists of fourteen negatively. This presentation is a very informative piece on pn junction diode an important part of electronics education. Note to those familiar with a diode turn on voltage. A pn junction diode is twoterminal or twoelectrode semiconductor device, which allows the electric current in only one direction while blocks the electric current in opposite or reverse direction. Pdf on dec 31, 2011, toshifumi sugiura and others published barrier potential across semiconductor pn.
Abrupt depletion layer approximation let apply bias and calculate current through the pn junction currents in pn junction from sze, 1981. How a pn junction formed in a diode instrumentation tools. Pn junction diode and its characteristics in chapter 1 understanding the pn junction, we have seen how a pn junction is formed from a ptype and ntype semiconductor. Laser diode pn junction is formed by two layers of doped gallium arsenide it is forward biased laser diodes and photodiodes are used in the pick up system of compact disk cd. No generationrecombination in the depletion layer 6. Pdf the excerpts presented, from the authors book crystal fire, track the work of an. Formation and properties of junction diode physics youtube. In order to initiate the junction formation, click the formjunction button or mouse drag one object toward the other. A pn junction is a junction formed by joining ptype and ntype semiconductors together in very close contact. However, in a pn junction, when the electrons and holes move to the other side of the junction, they leave behind exposed charges on dopant atom sites, which are fixed in the crystal lattice and are unable to move. At the point of the junction, which we call the metallurgical junction, is where n d n a 0.
Draw the vi characteristics of pn junction diode and explain the operation of diodes as with other semiconductor devices is often described by a special graph called a characteristic curve. Being free particles, electrons start diffusing from ntype material into pmaterial being free particles, holes, too, start diffusing from ptype material into nmaterial have they been neutral particles, eventually all the free electrons. The pn junction biasing the pn junction the diode trouble shooting. When ptype and ntype materials are placed in contact with each other, the junction behaves very differently than either type of material alone.
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. Specifically, current will flow readily in one direction forward biased but not in the other reverse biased, creating the basic diode. These are the easiest and basic diodes available in and use pn junction characteristics like depletion layer, diffusion and drift current. A pn junction is a device formed by joining p type doped with b, al with ntype doped with p. 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. Similarly, holes flow by diffusion from the ptype side to the ntype side. Pn junction underbiasing 14 boltzmanns approximation. The energy gap between the valence level and the conduction level is midway between that of insulators and conductors such as metals, and thermal energy causes. Pn junction diode pn junction semiconductors scribd. Pn junctions consist of two semiconductor regions of opposite type.
Formation of a pn junction diode and its band diagram. Pn junction is a significant building block and it is one among the indispensable structures. The combination of ptype and ntype semiconductors results in a junction. The pn junction diode is the typical diode that has been used in the previous circuits. 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.
When the ptype and ntype materials come together, there is a non equilibrium state of. E photolithography photolithography is a process by which we get the proper structure of the device on the wafer. 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. It is used in the construction of transistors, fet, gates and many other types of integrated circuits. Drift pn junction diodes log in or register to post comments. A pn junction diode is a twoterminal electronics element, which can be classified as either step graded or linear graded. 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. The charge plasma pn diode university of twente research.
I have developed a second chapter on the series, which explains the characteristics of pn junction diode. As shown in the figure, pn junction diode is a 2 terminal polarity sensitive device. With the formation of the p and n materials combination of electrons and holes at the. Hence, a depletion layer is formed that is not chargeneutral. The pn junction is the fundamental building block of the electronic age. As the depletion layer built up a different of potential appears across the junction this difference of potential at junction is called potential barrier. This recombination of electrons and holes produces a narrow region at junction called depletion layer. There are three biasing conditions for pn junction diode and this is based on the voltage applied. The behaviour of the pn junction with regards to the potential barriers width produces an asymmetrical conducting two terminal device, better known as the pn junction diode. Pn junction one of the crucial keys to solid state electronics is the nature of the pn junction. A pn junction is a device formed by joining ptype doped with b, al with ntype doped with p.
Pn junction diode applications pn diode applications. When the diode is forwardbiased, it can be used in led lighting applications. How a pn junction formed in a diode engineering tutorial. A pn junction is the metallurgical boundary between the n and pregions of a semiconductor crystal. Lecture 15 the pn junction diode i iv characteristics november 1, 2005 contents. Semiconductor pnjunction diodes physically, diodes are formed by the interface between two regions of oppositely doped semiconductor i. Pn junction diode is one of the fundamental elements in electronics. Since a junction forms between a p type and n type material it is called as pn junction. This pn diode applications are very useful for beginners. 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. Review, pn junctions, fermi levels, forward bias prof j. P type and n type semiconductors, takenseparately are of very limited use. A pn junction with open terminals excluding minority carriers f. Now, if we join the two types of semiconductors ptype and ntype together then a new device is formed called as pn junction diode.
A k schematic symbol for a pn junction diode p n representative structure for a pn junction diode. Pn junction diode free download as powerpoint presentation. To return the semiconductor to separate pieces, click the separate button. This nonneutral region produces an electric field, producing a drift current that flows. This page of application notes section covers pn junction diode applications. Please refer the applet to know the fabrication process of the diode. Smith department of eecs university of california, berkeley eecs 105 spring 2004, lecture 19 prof. Explain the formation of potential barrier and depletion layer.
Lets look at how a pn junction is formed and how it behaves under a bias or an externally applied voltage. Pn junction tutorial introduction to pn junction diodes. This is a two terminal device consisting of a pn junction formed either in ge. Simplified physical structure construction on a cmos chip.
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