It is acting as normal diode while forward biasing. Using this process for silicon diodes produces two differently doped layers of silicon, which form a pn junction. No generationrecombination in the depletion layer 6. Pn junctions are formed in various kinds of semiconductor devices by several techniques. Working of pn junction diode with biasing, characteristics. Such junctions show a pronounced rectifying behavior. Feb 20, 2018 diode current equation diode equation thermal voltage and ideality factor diode duration. In the case of normal diodes the diode damages at the break down voltage. When carriers are injected across a forwardbiased junction, it emits incoherent light. This document is highly rated by electrical engineering ee students and has been viewed 1949 times. Zero bias no external voltage is applied to the pn junction diode. 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.
A very small current will made at the junction due to the movement of minority charge carriers across the junction. When the diode is forwardbiased, it can be used in led lighting applications. They are also called pn diodes in analogy with vacuum diodes. The name diode is derived from diode which means a device that has two electrodes. Semiconductors pn junction theory interview questions and answers pdf free download posted on august 19, 2018 june 24, 2019 by engineer 6 comments posted in semiconductors pn junction theory interview questions. 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. And based on the applied voltage, there are three possible biasing conditions for the pn junction diode, which are as follows.
This allows electrical current to pass through the junction only. The pn junction solidstate device theory electronics. Diode theory diode as a conductor when a voltage is applied current will flow. The crosssection in figure aboveb looks a bit more complex than a simple pn junction. 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. The diode is firmed by doping a semiconductor like silicon or germanium with trivalent impurity e. 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. 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. Also in the next tutorial we will examine the signal diode static currentvoltage characteristics curve and parameters. What happens when we join ptype and ntype semiconductors. In a junction diode a the depletion capacitance increases with increase in the reverse bias b the depletion capacitance decreases with increase in the reverse bias. The recombination at the junction allows battery current to flow through the pn junction diode.
A diode allow electric current to pass in forward direction and block current in reverse direction. Chapter 1 semiconductor pn junction theory and applications. Understanding about the pn junction diode theory and. We have seen how a diode is made with p and n semiconductors but. Pn junction diode and characteristics of pn junction diode. The vi characteristic of pn junction diode indicates that the forward current is negligible up to the knee voltage. Kasap, 1990 2001 an ebooklet 1 pn junction the shockley model safa kasap department of electrical engineering university of saskatchewan canada although the hole and its negative counterpart, the excess electron, have been prominent in the theory of solids since the work of a. Pn junction tutorial introduction to pn junction diodes. A light emitting diode led is essentially a pn junction diode. A pn junction diode is a twoterminal electronics element, which can be classified as either step graded or linear graded. 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. In pn junction diode, when ptype and ntype regions are joined.
Jan 29, 2019 pn junction diode is one of the fundamental elements in electronics. Review, pn junctions, fermi levels, forward bias prof j. Theory a semiconductor pn junction diode is a two terminal electronic device that allows current in only one direction. Apr 29, 2020 quantitative theory of pn junction diode electrical engineering ee notes edurev is made by best teachers of electrical engineering ee.
Zener diode is a pn junction diode specially designed to operate in the reverse biased mode. The result is that some of the free electrons from the donor impurity atoms begi. A semiconductor diode is the most common type diode, which is a piece of semiconductor material with a pn junction connected to two terminals. To plot voltampere characteristics of silicon pn junction diode. A pn junction diode is made by forming a ptype region of material directly next to a ntype region. Conventional current flows from positive to negative. Thus, v 10v when the voltage is reversed the p n junction is switched from conduction state. Definition, symbol, and types of diodes electrical4u. Range of tunnel diode voltage for which the slope of the characteristics is ve is between v p and v v option c 11. Hbd854 zener theory and design considerations handbook. Semiconductor theory the active portion of a zener diode is a semiconductor pn junction. When a reverse voltage is applied to a conventional pn junction diode and the voltage is increased it will eventually breakdown and it will be subject to high current due to avalanche breakdown. Also, it explains the phenomenon of shockleyqueisser limit.
The depletion region shrinks allowing current to flow. This causes the holes to move toward the depletion region and the free electrons to move toward the depletion region. Hence comparing the schematic symbol to the pn junction in figure 4, we see the anode is the ptype semiconductor and the cathode is the ntype semiconductor. The symbols for diodes and transistors use arrows to indi cate the direction that conventional current can flow. 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. Questions you should be able to answer by the end of todays lecture. Pn junction diode is one of the fundamental elements in electronics. 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. This article discusses about pn junction diode, diode theory of zero bias, forward bias, reverse bias with vi characteristics and its applications. 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. Among these are the widely used techniques known as alloying and diffusion which are utilized in fabricating zener pn junctions to provide excellent control over zener.
This is the basic construction of the pn junction diode. If this current is not limited by the surrounding circuitry, the diode is very likely to be destroyed because of. This lecture uncovers the basic science of semiconductor devices and solar cells, including pn junction and photovoltaic effects. Dec 21, 2018 and this junction is known as the pn junction. 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. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction.
Most of the commercial leds are realized using a highly doped n and a p junction. It has a particular voltage known as break down voltage, at which the diode break downs while reverse biased. P n junction theory and diodes part ii gate problems. Review of basic semiconductor and pn junction theory. The direction of arrow is the direction of conventional current flow under forward bias. The pnjunction is the root for semiconductor diodes. 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. 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. Simplified physical structure construction on a cmos chip. Abrupt depletion layer approximation let apply bias and calculate current through the pn junction currents in pn junction from sze, 1981. Undoped or intrinsic silicon has a lattice structure of atoms, each having four valence electrons, but p type silicon and. Now lets try applying an external voltage to the pn junction diode.
The symbolic representation of the diode is as follows. The pn junction diode is the basic semiconductor diode format. Boron or aluminium from one end to form ptype region and with pentavalent impurity like. A pn junction is the simplest form of the semiconductor diode. A pn junction is the metallurgical boundary between the n and pregions of a semiconductor crystal. The diode is firmed by doping a semiconductor like silicon or germanium with. 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. Quantitative theory of pn junction diode electrical. A pn junction diode is a twoterminal electronics element, which can be classified as either. Pn junction diode and diode characteristics electronicstutorials.
The behaviour of a diode in a circuit is given by its iv characteristics. Silicon a single silicon atom consists of fourteen negatively. Donor impurities pentavalent are introduced into oneside and acceptor impurities. 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. Theoretical background semiconductor diode theory is. P n junction theory and diodes part i gate problems 1. Dec 27, 2017 the symbolic representation of the diode is as follows. Jan 04, 2020 a pn junction is the simplest form of the semiconductor diode. Junction diodes solidstate device theory electronics. The circuit schematic symbol of a diode is shown in figure 5. Vi characteristics of pn junction diode in 3biasing modes. In this type of diode, we dope one side of a semiconductor piece with an acceptor impurity and another side with a donor impurity.
A pnjunction is formed when an ntype material is fused together with a ptype material creating a semiconductor diode. Diode schematic symbol and actual picture of a common 1n914 diode the black stripe in the picture is the cathode. Pn junction theory for semiconductor diodes electronicstutorials. Diode current equation diode equation thermal voltage and ideality factor diode duration. 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. Pn junctions consist of two semiconductor regions of opposite type. Junction coming to the equilibrium by balancing the fermi level ef ef the balance is achieved by electrons diffusing into a pside bringing an extra negative charge in there and by the holes diffusing into an nside bringing an extra negative charge in there pn.
P n junction theory and diodes part i gate problems. The pn junction is a versatile element, which can be used as a. 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. Image source forward biasing a pn junction diode is very simple. We can then fill in the junction region of the band diagram as. Theory of pn junction diode, diode current equation. It is the most essential and the basic building block of the electronic device. 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. A pn junction is a boundary or interface between two types of semiconductor materials, ptype and ntype, inside a single crystal of semiconductor. Zero bias no external voltage potential is applied to the pn junction diode. Smith department of eecs university of california, berkeley eecs 105 spring 2004, lecture 19 prof. Iv characteristics pn junction diode theory a semiconductor pn junction diode is a two terminal electronic device that allows current in only one direction.
The pn junction has the very useful property that electrons are only able to flow in one direction. It generally shows the relation between bias voltage and current of a diode. The pn junction is the fundamental building block of the electronic age. The pn junction is the root for semiconductor diodes. P type and n type semiconductors, takenseparately are of very limited use. It is one of the simplest semiconductor devices as it allows current to flow in only one direction. A order flows through the diode and it increases gradually to maximum at large reverse voltage. The vi characteristics of a diode can be forward or reverse. Pn junction diode baising and its vi characteristics. It is the most fundamental device element that forms the basis of many electronic devices such as pn diodes, optoelectronic devices like lightemitting diode and photodetector, field.
Pn junction theory a pn junction 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. 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. If a conventional pn junction diode is run into reverse breakdown it is most likely to be irreparably damaged. A p n junction is in series with 100 ohms resistor p n junction is basically a diode. A simplified planar silicon diode is illustrated in fig. A pn junction with open terminals excluding minority carriers f. If a diode is forward biased as in figure abovea, the current will increase slightly as the voltage is increased from 0 v. 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.
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