A pnjunction is formed when an ntype material is fused together with a ptype material creating a semiconductor diode. 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. Let us now try to know what happens if a diode is connected in forward biased and in reverse biased conditions. Transistor and diode studies static properties of this type of diode structure was made, and numerical computations are being completed. The junction formed here is because of its terminals are the emitter and the base as well as the collector and the base. An ntype semiconductor has plenty of free electrons and a very few numbers of holes. The conversion of alternating current into direct current is known as rectification.
Ee lecture notes university of california, berkeley. The pn junction is the fundamental building block of the electronic age. A diodes working principle depends on the interaction of ntype and ptype semico nductors. Shockley diode circuit with working and characteristics. It is constructed of a p and an n junction connected together. A pn junction is a boundary or interface between two types of semiconductor materials, ptype and ntype, inside a single crystal of semiconductor. Such junctions show a pronounced rectifying behavior. Working of pn junction diode with biasing, characteristics. Here we will describe the system characteristics of the bjt. Working of the zener diode is similar to a pn junction diode in forwarding biased condition, but the. By watching this video, you will learn the following. Apr 05, 2019 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. Pn junctions worksheet discrete semiconductor devices.
In this article, we are going to explain zener diode and its applications in detail. Pn junction theory for semiconductor diodes electronicstutorials. A diodes oneway gate feature does not work all the time. Animation how a p n junction semiconductor works forward. May 19, 2014 how diode works, animation diode, animation pn junction, working of pn junction, how does a pn junction semiconductor works, what is avalanche breakdown, what is drift current, how drift current. In a small silicon diode operating at its rated currents, the voltage drop is. 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. Now, if we join the two types of semiconductors ptype and ntype together then a new device is formed called as pn junction diode.
This article discusses about pn junction diode, diode theory of zero bias, forward bias, reverse bias with vi characteristics and its applications. The application of the shockley diode is a relaxation oscillator circuit that is shown above. Diode pn junction when p and n type silicon are brought together during manufacture, a junction is created where the p type and n type materials meet, and holes close to the junction in the p. Reverse bias of pn junction when the voltage is applied this way round it tends to pull the free electrons and holes apart, and increases the height of the energy barrier between the two sides. This fact is emphasized so strongly in many textbooks that students usually dont think to ask when they measure a diodes forward voltage drop and find it to be considerably different than 0. 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. The width of the depletion region of the cb junction is higher than the be junction. I s pn junction saturation current, in amps typically 1 picoamp. When the potential formed by the widened depletion layer equals the applied voltage, the current will cease except for the small thermal current. If this reverse biased voltage across the diode is increased continually, the depletion layer becomes more and more wider. Diode operation no current flows because the holes and electrons are moving in the wrong direction. Pn junctions consist of two semiconductor regions of opposite type. Where four layers are pnpn and two terminals are anode and cathode. When the diode is forwardbiased, it can be used in led lighting applications.
For a silicon diode this voltage is approximately 0. Solve each circuit with its corresponding diode equation. In our previous articles, we explain in detail about diodes, pn junction diode, semiconductors etc. Before going to the working, i would like to explain.
How diode works, animation diode, animation pn junction, working of pn junction, how does a pn junction semiconductor works, what is avalanche breakdown, what is drift. When revrese voltage is increased beyond a value,called breakdown voltage,the reverse current increases sharply and the diode shows almost zero resistance. When forward biased, a small voltage is required to get the diode current flowing. We can then fill in the junction region of the band diagram as. By exploring the electrical properties of silicon, it is possible to acquire an. Before going to the working, i would like to explain how exactly the junction diode is made. Lecture 15 the pn junction diode i mit opencourseware. The increase in resistance of the pn junction results in the junction behaving as an insulator. The major difference between pn junction and the zener diode is that the pn junction diode allows current to pass only in the forward direction, whereas the zener diode allows the current to flow both in the forward and the reversed direction. Use the inequality for that diode state range of validity to find the range of circuit variable which leads to that state. 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.
A pn junction diode meant to operate in the break down region is called a zener diode. Silicon a single silicon atom consists of fourteen negatively. Pn junction diode baising and its vi characteristics. It is one of the simplest semiconductor devices as. The function of the shockley diode is similar to a normal diode without any initiate ips.
In other words, we can say that the concentration of free electrons is high and that of holes is very low in an ntype semiconductor. Reverse bias of pn junction when the voltage is applied this way round it tends to pull the free electrons and holes apart, and increases the height of the energy barrier between the two sides of the diode. The other differences between the pn junction and zener diode are explained below in the comparison chart. Dec 27, 2017 its working principle is when the diode is reverse biased, small leakage currents pass through the diode, when the reverse voltage is further increased the leakage current also increases which are fast enough to break few covalent bonds within the junction these new charge carriers further breaks down the remaining covalent bonds causing huge. How a pnjunction diode works university of st andrews. Reverse voltage above 25 v destroys the junction permanentaly. The term junction implies the boundary or region of transition between n type and p type semiconductor material. The pn junction diode the nature of the pn junction is that it will conduct current in the forward direction but not in the reverse direction. Semiconductor pn junction diodes physically, diodes are formed by the interface between two regions of oppositely doped semiconductor i. The emitterbase diode is connected in the forwardbias, whereas the collectorbase diode is connected in the reversedbias. 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. Bring them together and join them to make one piece of semiconductor which is doped differently either side of the junction. A pn junction diode is made of a crystal of semiconductor, usually silicon.
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. A pn junction is a boundary or interface between two types of semiconductor materials, ptype. 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. The be junction is forward bias and the cb is a reverse bias junction. This article provides a more detailed explanation of pn diode behavior than that found in the articles pn junction or diode. Investigation of a barrier layer by the thermoprobe method pdf. 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. Jul 27, 2015 the shockley diode is a two terminal and four layer semiconductor switching diode. A pn diode is a type of semiconductor diode based upon the pn junction. Zener diode is a special kind of diode which permits the flow of current in the forward direction as well as in reverse direction when the voltage is above a certain voltage known as breakdown or zener voltage. When a pn junction diode is reverse biased, the depletion layer becomes wider.
A pn junction diode allows electric charges to flow in one direction, but not in. Pn junctions worksheet discrete semiconductor devices and. Understanding about the pn junction diode theory and working. Bias is the application of a voltage across a pn junction. A pn junction is the metallurgical boundary between the n and pregions of a semiconductor crystal. A diode cannot conduct in reverse biased condition. This is the basic construction of the pn junction diode. Bipolar junction transistors bjt general configuration and definitions the transistor is the main building block element of electronics. The pn junction diode is the basic semiconductor diode format. Pn junction diode explained forward bias and reverse bias.
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. When an external voltage is applied to a diode such that it cancels the potential barrier and permits the flow of current is called as forward bias. 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. It is a semiconductor device and it comes in two general types. The pn junction is a versatile element, which can be used as a. Zener diode working, characteristics and application as. Pn junction tutorial introduction to pn junction diodes. 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.
Working of a pn junction current iv characteristic of reverse bias a pn junction diode. Zener diodes are normal pn junction diodes operating in a reversebiased condition. It is one of the simplest semiconductor devices as it allows current to flow in only one direction. To understand how a pn junction diode works, begin by imagining two separate bits of semiconductor, one ntype, the other ptype. Ive tried to make this explanation as simple as possible so that no conceptual doubts arise. The diode conducts current in only one direction, and it is made by joining a ptype semiconducting layer to an ntype semiconducting. A pnjunction diode is formed by joining together ntype and ptype silicon. Draw the vi characteristics of pn junction diode and explain the operation of. From the above, it follows that zero power dissipation occurs in an ideal diode. The bipolar junction transistors consist of two types of transistors. The pn junction has the very useful property that electrons are only able to flow in one direction. To understand how a pnjunction diode works, begin by imagining two separate bits of semiconductor, one ntype, the other ptype. Calculate the ideal diode current assuming that the ntype region is much smaller than the.
As a result it is almost impossible for any electrons or holes to cross the depletion zone and the diode current produced is virtually zero. A pn junction diode is made by forming a ptype region of material directly next to a ntype region. Junction transistors bjts there are two types of bjts, the npn and pnp the two junctions are termed the baseemitter junction and the basecollector junction in order for the transistor to operate properly, the two junctions must have the correct dc bias voltages the baseemitter be junction is forward biased. And the working of this pn junction diode under forward and reverse bias has been explained. If this reverse biased voltage across the diode is increased. Understanding the pn junction university of new south wales.
Apr 07, 20 when revrese voltage is increased beyond a value,called breakdown voltage,the reverse current increases sharply and the diode shows almost zero resistance. The junction in between the terminals of the emitter and the base is biased in forwarding condition. The zener diode working principles and its various applications. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction. Diode pn junction when p and n type silicon are brought together during manufacture, a junction is created where the p type and n type materials meet, and holes close to the junction in the p type silicon are attracted into negatively charged n type material at the other side of the junction. They are also called pn diodes in analogy with vacuum diodes. It is therefore a basic tool for rectification in the. Due to this characteristic, the diode finds number of applications as given below.
Pnp transistor basics construction, working principle. Understand the physics of a pnjunction and how a junction diode is created 2. Definition, symbol, and types of diodes electrical4u. There are two operating regions and three possible biasing conditions for the standard junction diode and these are. It is used for many forms of rectification for current levels both large and small, as well as high and low voltage levels, and. Ive seen too many students gain the false impression that silicon pn junctions always drop 0. Semiconductor principles were unknown to the developers of these early. An abrupt silicon pn junction n a 10 16 cm3 and n d 4 x 10 16 cm3 is biased with v a 0. Semiconductor pnjunction diodes physically, diodes are formed by the interface between two regions of oppositely doped semiconductor i. Questions you should be able to answer by the end of todays lecture.
An ntype semiconductor has plenty of free electrons. What happens when we join ptype and ntype semiconductors. Parametric solution of diode circuits is desirable. The zener diode working principles and its various. In this bipolar junction transistor, the voltage across the emitterbase junction that is in forwardbias is always less than the collectorbase junction reversedbias. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner work ings of the pn junction. Working of the zener diode is similar to a pn junction diode in forwarding biased condition, but the uniqueness lies in the fact that it can also conduct when it is connected in reverse bias above its thresholdbreakdown voltage. Understand the behaviour of a diode under forward and reverse bias and be able to plot the iv characteristic of. 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 diode the diode is a two terminal semiconductor device that allows current to flow in only one direction.
Zener diode is a special kind of diode which permits the flow of current in the forward direction as well as in reverse direction when the voltage is above a certain voltage known as breakdown or. Where, i d current through the pn junction, in amps. As it is in forwarding mode the majority carriers here are the holes these get inserted into the base region. A diode is a twoterminal electronic component that conducts current primarily in one direction.
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