Semiconductors with higher carrier mobility and carrier density are required to fabricate a pn junction diode for highspeed device operation and highfrequency signal processing. P n junction diode theory pdf the p n junction is the fundamental building block of the electronic. Semiconductors are materials with electrical conductivity intermediate between that of a conductor and an insulator. It has a particular voltage known as break down voltage, at which the diode break downs while reverse biased. Silicon a single silicon atom consists of fourteen negatively. The led is a special type of diode and they have similar electrical characteristics of a pn junction diode. A zener diode when forward biased behaves like an ordinary p n junction diode.
In a forward biased p n junction, the sequence of events that best describes the mechanism of current flow is a injection, and subsequent diffusion and recombination of minority. 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. P n junction theory and diodes part ii gate problems. The theory for the pn junction diode was developed by shockley in 1949,3 and it was instrumental for the invention of the bipolar junction transistor. When a photon of sufficient energy strikes the diode, it creates an electronhole pair.
Jan 29, 2019 a pn junction diode is a twoterminal electronics element, which can be classified as either step graded or linear graded. You just need to take a battery whose values can be varied from o to v volts, connect its positive terminal to the p side of pn junction diode and then connect the negative terminal of battery to the n side of the pn junction diode. Electronics tutorial describing the semiconductor pn junction and pn junction theory of semiconductor ntype and ptype materials. In a junction diode a the depletion capacitance increases with increase in the reverse bias. They are also called p n diodes in analogy with vacuum diodes. 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. This article discusses about pn junction diode, diode theory of zero bias, forward bias, reverse bias with vi characteristics and its applications. Junction diodes solidstate device theory electronics. 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. They are referred to as photoelectrons and photoholes the applied voltage separates the photocarriers attracting electrons toward. A p n 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.
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. The same number of minority carriers are being swept. Majority carriers can diffuse across the pn junction depletion region, even though the electric field impedes their crossing. Questions you should be able to answer by the end of todays lecture. Low injection fermi level do not change in the depletion layer minority carrier densities p n junction diode n type material p type material n type material p type material a p n junction diode is made by forming a p type. Scribd is the worlds largest social reading and publishing site. Instead, a diode will have negligible resistance in one direction to allow current flow, and a very high resistance in the reverse direction to prevent current flow. Pn junction theory 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. Smith department of eecs university of california, berkeley eecs 105 spring 2004. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction. P n junction diode theory pdf the pn junction is the fundamental building block of the electronic. The objective of this experiment is to measure the iv curve for pn junction diode and to understand the characteristics of pn junction. An ideal pn junction diode does not conduct in reverse biased condition. And the working of this pn junction diode under forward and reverse bias has been.
As the pn junction is formed, holes from p region diffuse across the junction and recombine with the electrons in the n region near the junction resulting. Pn junction diode baising and its vi characteristics. If the diode is forward biased, it allows the electric current flow. The p n junction is a versatile element, which can be used as a. A diodes working principle depends on the interaction of ntype and ptype semico nductors. The concept to be made clear is that the pointcontact diode preceded the junction diode and modern semiconductors by several decades. If the positive terminal of the battery is connected to the p type semiconductor and the negative terminal of the battery is connected to the n type semiconductor, the diode is said to be in forward bias. The diode is simple in its basic concept, being formed from the junction of ntype and ptype materials, although in reality the manufacture and theory of operation are more complex.
Explain the formation of potential barrier and depletion layer. They are also called pn diodes in analogy with vacuum diodes. Just by going through these short questions and answers, you will cover a large portion of the chapter itself. Even to this day, the pointcontact diode is a practical means of microwave frequency detection because of its low capacitance. Like any diode, the pn junction diode has two connections or electrodes. Lightemitting diodes circuit, working principle and application. It is acting as normal diode while forward biasing.
Image source forward biasing a pn junction diode is very simple. Chemically doped random network carbon nanotube pn. The horizontal line in the below figure represents the amount of voltage applied across the pn junction diode whereas the vertical line represents the amount of current flows in the pn junction diode. 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. Also in the next tutorial we will examine the signal diode static currentvoltage characteristics curve and parameters. This is the basic construction of the pn junction diode.
P type and n type semiconductors, takenseparately are of very limited use. Theoretical background semiconductor diode theory is. We will assume, unless stated otherwise, that the doped regions are uniformly doped and that the transition between the two regions is abrupt. The forwardbias and the reversebias properties of the p n junction imply that it can be used as a diode. Shockley theory minority carrier concentrations at the edges of the depletion region will serve as boundary conditions.
A pn junction is a boundary or interface between two types of semiconductor materials, ptype. Varactor theory free download as powerpoint presentation. Pn junction diode is integral for all electronic devices to operate, aggregating all forms of carrier transport, generation, and recombination. An ideal p n junction diode does not conduct in reverse biased condition. Jul 31, 2017 in this physics digital electronics video lecture in hindi for class 12 we explained forward and reverse bias in p n junction diode in terms of depletion layer and potential barrier.
The theory of pn junctions in semiconductors and pn junction transistors. 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 and therefore we can not described its operation by simply using an equation such as ohms law. Jul 28, 2016 when the n type semiconductor and p type semiconductor materials are first joined together a very large density gradient exists between both sides of the pn junction. Forward biasing a pn junction diode is very simple. A p n junction is in series with 100 ohms resistor p n junction is basically a diode. A semiconductor pn junction diode is a two terminal electronic device that allows current in only one direction.
This is the basic construction of the p n junction diode. A diode is effectively like a valve for an electrical circuit semiconductor diodes are the most common type of diode. Majority carriers can diffuse across the p n junction depletion region, even though the electric field impedes their crossing. To draw the iv characteristic curve of a pn junction diode in forward bias and reverse bias. Zener diode is a pn junction diode specially designed to operate in the reverse biased mode. In this video, the pn junction diode has been explained. What happens when we join ptype and ntype semiconductors. When the diode is forwardbiased, it can be used in led lighting applications. P n junctions consist of two semiconductor regions of opposite type. The pn junction has been the most common rectifier used in. Pn junction theory 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. Electronics tutorial describing the semiconductor pn junction and pn junction theory of semiconductor n type and p type materials. Here, we use a chemically doped semiconducting singlewalled carbon nanotube swcnt random network for a field effect transistor fet and demonstrate a rectifier operated at a wide range of frequencies by.
Electronics questions and answers by sasmita march 27, 2019. The term junction refers to the boundary interface where the two regions of the semiconductor meet. Frequently we will deal with pn junctions in which one side is. P n junction theory and diodes part i gate problems. A light emitting diode led is essentially a pn junction diode. Now lets try applying an external voltage to the pn junction diode. The p n junction has been the most common rectifier used in. Under forward bias electrons are injected from n region to p region and holes are injected form p region into the n region. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the p n junction. Pn junction diode explained forward bias and reverse bias. P517617 lec5, p1 diodes and transistors diodes what do we use diodes for.
Pn junctions consist of two semiconductor regions of opposite type. Pn junction is formed in a single crystal by joining two ntype and ptype semiconductors. The diode is simple in its basic concept, being formed from the junction of n type and p type materials, although in reality the manufacture and theory of operation are more complex. Pn junction theory a pn junction is formed when an n type material is fused together with a p type material creating a semiconductor diode in the previous tutorial we saw how to make an n type semiconductor material by doping a silicon atom with small amounts of antimony and also how to make a p type semiconductor material by doping another. A pn junction is the metallurgical boundary between the n and pregions of a semiconductor crystal. We will refer to this structure as an abrupt pn junction. The theory for the p n junction diode was developed by shockley in 1949,3 and it was instrumental for the invention of the bipolar junction transistor. A pn junction is a junction formed by joining ptype and ntype semiconductors together in very close contact. A pn junction is a boundary or interface between two types of semiconductor materials, ptype and ntype, inside a single crystal of semiconductor. Pn junction tutorial introduction to pn junction diodes. Pn junction diode and characteristics of pn junction diode.
This presentation is a very informative piece on pn junction diode an important part of electronics education. A p n junction is the metallurgical boundary between the n and p regions of a semiconductor crystal. P517617 lec 5, p7 transistors transistors are the heart of modern electronics replaced vacuum tubes voltage and current amplifier circuits high frequency switching computers impedance matching low power small size, can pack thousands of transistors in mm2 in this class we will only consider bipolar transistors. The transfer of electrons from the n side of the junction to holes annihilated on the p side of the junction produces a barrier voltage. 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. We have seen how a diode is made with p and n semiconductors but we need to know what happens inside it to form a unique property of allowing current in only one direction and what happens at the exact point of contact initially at its junction. A zener diode conducts excellently even in reverse biased condition. Definition, symbol, and types of diodes electrical4u. In 1962, nick holonyak has come up with an idea of light emitting diode, and he was working for the general electric company. Such junctions show a pronounced rectifying behavior.
In this physics digital electronics video lecture in hindi for class 12 we explained forward and reverse bias in pn junction diode in terms of depletion layer and potential barrier. If a battery is connected to a diode, current will flow. If the absorption occurs in the junctions depletion region, or one diffusion length away from it, these carriers are swept from the junction by the builtin electric. These diodes operate at a precise value of voltage called break down voltage.
The vi characteristics or voltagecurrent characteristics of the pn junction diode is shown in the below figure. The pn junction solidstate device theory electronics. 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. The pn junction provides satisfactory performance when operated within these limiting values. The p n junction is the fundamental building block of the electronic age. The result is that some of the free electrons from the donor impurity atoms begi. A p n junction diode is formed by doping one side of a piece of silicon with a p type dopant boran and the other side with a n type dopant phosphorus. The light emitting diode is a twolead semiconductor light source. The contact surface between the layers of ptype and ntype semiconductor pieces plated together so as. Pn junctions are fabricated from a monocrystalline piece of semiconductor with both a p type and n type region in proximity at a junction. When carriers are injected across a forwardbiased junction, it emits incoherent light.
Field at the junction and it is this electric field that is the basis of the operation of diodes. P n junction theory and diodes part i gate problems 1. A pn junction diode is a twoterminal electronics element, which can be classified as either step graded or linear graded. Photodetectors pn junction can detect light when reverse biased ptype ntype when the light illuminates the pn junction, the photons energy releases free electrons and holes. Although in the real world, diodes can not achieve zero or infinite resistance. Conventional current flows from positive to negative and is opposite to the direction that electron current flows. Apr 05, 2019 pn junction is formed in a single crystal by joining two n type and p type semiconductors. Please refer the applet to know the fabrication process of the diode. Most of the commercial leds are realized using a highly doped n and a p junction. The diode is firmed by doping a semiconductor like silicon or germanium with trivalent impurity e. The objective of this experiment is to measure the iv curve for p n junction diode and to understand the characteristics of p n junction. The pn junction diode may get destroyed due to excessive heat if any of these values are exceeded. In a step graded pn junction diode, the concentration of dopants both, in the n side and the p side are uniform up to the junction. Thus, v 10v when the voltage is reversed the p n junction is switched from conduction state.
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. P n junction diode is integral for all electronic devices to operate, aggregating all forms of carrier transport, generation, and recombination. The direction of arrow is the direction of conventional current flow under forward bias. The diode is firmed by doping a semiconductor like silicon or germanium with. Pn junction diode baising and its vi characteristics elprocus. A p n junction diode allows electric charges to flow in one direction, but not in the opposite direction. Pn junction diode is a two terminal device, the characteristics of diode depends on the polarity of the external potential applied to the pn junction diode. Zener diode is a p n junction diode specially designed to operate in the reverse biased mode. Review, pn junctions, fermi levels, forward bias prof j. Holes drift into nmaterial and find plenty of electrons there. An ntype semiconductor has plenty of free electrons and a very few numbers of holes.