Pn junction diode is a diode which can be used as a rectifier, logic gate, voltage stabiliser, switching device, voltage dependent capacitor and in optoelectronics as a photodiode, lightemitting diode led, laser diode, photo detector, or solar cell in electronics. Definition, symbol, and types of diodes electrical4u. From the above, it follows that zero power dissipation occurs in an ideal diode. Reverse voltage above 25 v destroys the junction permanentaly. 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. A pn junction diode is a twoterminal electronics element, which can be classified as either step graded or linear graded. To understand how a pnjunction diode works, begin by imagining two separate bits of semiconductor, one ntype, the other ptype. The slope of the pn junction diode in forwarding bias shows the resistance is very low. Pn junction diode is a device made of two semiconductor material joined together with the required amount of impurity.
By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction. The vi characteristics or voltagecurrent characteristics of the pn junction diode is shown in the below figure. The pn junction has the very useful property that electrons are only able to flow in one direction. However, at normal operating temperatures, this small current may be. Calculate the ideal diode current assuming that the ntype region is much smaller than the diffusion length with w n 1 mm and assuming a long ptype region. Semiconductor pnjunction diodes physically, diodes are formed by the interface between two regions of oppositely doped semiconductor i.
The conversion of alternating current into direct current is known as rectification. Image source forward biasing a pn junction diode is very simple. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner work ings of the pn junction. The vi characteristics of pn junction diode in forwarding bias are nonlinear, that is, not a straight line. The point contact diodes are suitable for operation at microwave range while the junction diodes are. A k schematic symbol for a pn junction diode p n representative structure for a pn junction diode zener diodes. Due to this characteristic, the diode finds number of applications as given below. 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. 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. As shown in the figure, pn junction diode is a 2 terminal polarity sensitive device. Recipe for solving diode circuits state of diode is unknown before solving the circuit 1. A pn junction is a junction formed by joining ptype and ntype semiconductors together in very close contact. Pn junction diode applications pn diode applications.
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. 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. Unbiased pn junction, forward biased pn junction and reversed biased pn junction. What is the difference between pnp and npn transistor.
This page of application notes section covers pn junction diode applications. Pn junction diode and characteristics of pn junction diode. The pn junction diode is the basic semiconductor diode format. Write down all circuit equations and simplify as much as possible 2. Pn junction forward bias reverse bias zener diodes duration. P n junction diode a pn junction is known as semiconductor diode.
This nonlinear characteristic illustrates that during the operation of the n junction, the resistance is not constant. To reverse bias a junction diode, the negative battery terminal is connected to the p. Pn junction tutorial introduction to pn junction diodes. P n junction diode pdf it is a twoterminal device consisting of. Navedtra 14027a construction electrician advanced part 5.
In ideal conditions, this pn junction behaves as a short circuit when it is forward biased, and as an open circuit when it is in the reverse biased. Vi characteristics of pn junction diode in 3biasing modes. A pn junction diode allows electric current when it is forward biased and blocks electric current when it is reverse biased. With proper biasing, pn diode allows current to flow in single direction. The working principle of a pn junction diode can be broadly understood under three categories. Are specifically designed to operate under reverse breakdown conditions. Some simple rules for getting transistors to work 1 for npn pnp collector must be more positive negative in voltage than emitter. An abrupt silicon pn junction n a 10 16 cm3 and n d 4 x 10 16 cm3 is biased with v a 0. 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.
Bring them together and join them to make one piece of semiconductor which is doped differently either side of the junction. At low current densities one can expect the pn diode to dominate the current flow, whereas at high current densities the nn. Before going to the working, i would like to explain. When revrese voltage is increased beyond a value,called breakdown voltage,the reverse current increases sharply and the diode shows almost zero resistance. Transistor and diode studies static properties of this type of diode structure was made, and numerical computations are being completed. Basic electronics special purpose diodes there are few diodes which are designed to serve some special purposes. A report including analyses of high injection in the forward direction, large reversevoltage conditions, and the behavior of the incremental. For example, a common type of transistor, the bipolar junction transistor, consists of two pn junctions in series, in the form npn or pnp. The fusion of these two diodes produces a three layer, two junction. Plot the vi characteristics and calculate the resistance levels. 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. Ive tried to make this explanation as simple as possible so that no conceptual doubts arise. A schottky junction is a special case of a pn junction, where metal serves the role of the ptype semiconductor.
This point contact diode operates on the same principle as junction diode. In this type of diode, we dope one side of a semiconductor piece with an acceptor impurity and another side with a donor impurity. The pn junction diode is the typical diode that has been used in the previous circuits. In addition,lets make the following simplifying assumptions. N type doping, p type doping, working of diode, working of npn transistor and dual stage amplification. The name diode is derived from diode which means a device that has two electrodes. A pn junction is the simplest form of the semiconductor diode. 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.
To study and verify the functionality of a pn junction diode in. The pn junction is the fundamental building block of the electronic age. Basic electronics special purpose diodes tutorialspoint. Questions you should be able to answer by the end of todays lecture. This pn diode applications are very useful for beginners. From the foregoing discussion the iv characteristics of a pn junction diode can be drawn as shown in fig. A pn junction is said to be formed only when a bonding force is created between the ptype and ntype semiconductor. The circuit symbol of pn junction diode is shown below. A pnjunction diode is formed by joining together ntype and ptype silicon. Silicon a single silicon atom consists of fourteen negatively. The diode conducts current in only one direction, and it is made by joining a ptype semiconducting layer to an ntype semiconducting layer semiconductor diodes have multiple uses. We also learnt that the junctions of the bipolar transistor can be biased in one of three different ways common base, common emitter.
The concentrations of free carriers injected into the quasineutral regions are small enough so that we can. Pn junction diode is one of the fundamental elements in electronics. This article provides a more detailed explanation of pn diode behavior than that found in the articles pn junction or diode a pn diode is a type of semiconductor diode based upon the pn junction. These diodes have a very accurate and specific reverse breakdown voltage. How a pnjunction diode works university of st andrews. An npn negativepositivenegative type and a pnp positivenegativepositive type the most commonly used transistor configuration is the npn transistor.
The term junction refers to the boundary interface where the two regions of the semiconductor meet. Working of a pn junction current iv characteristic of reverse bias a pn junction diode. Iv characteristics for silicon and germanium diodes is shown below. These materials are ntype, having electrons are majority carrier and ptype material, having holes are majority carrier. An ideal junction in which there are no generationrecombination processes in depletion region. When the n and ptype semiconductor materials are first joined together a very large density gradient exists between both sides of the junction so 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 material producing negative ions. The principle behind the test lies in the fact that little or no current will flow. Explain the formation of potential barrier and depletion layer.
In the year 1940 at bell labs, russell ohl was working with a silicon crystal to find out its properties. Npn transistor tutorial the bipolar npn transistor. In the previous tutorial we saw that the standard bipolar transistor or bjt, comes in two basic forms. Note to those familiar with a diode turn on voltage. Static characteristics of junction diode, point contact diode and. The extra valence electron of the phosphorus always is free electron. So, the base region actually works as the input and both the emitter and collector regions as output.
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