Filling a hole makes a negative ion and leaves behind a positive ion on the n side. 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 total charge on each side of a pn junction must be equal and opposite to maintain a neutral charge condition around the junction. A pn junction is the basic building block of many semiconductor devices like diodes, transistor etc. Pn junctions consist of two semiconductor regions of opposite type. 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. When you take a block of silicon and dope part of it with a trivalent impurity and the other part with a pentavalent impurity, a boundary called the pn junction is formed between the resulting ptype and ntype portions. P type and n type semiconductors, takenseparately are of very limited use. Fabrication of pnjunction diode by icfabrication process. Pn junction diode and characteristics of pn junction diode.
The pn junction is a versatile element, which can be used as a. A free powerpoint ppt presentation displayed as a flash slide show on id. What happens when we join ptype and ntype semiconductors. Note that a pnjunction diode cannot be made by simply pushing a piece of ptype against another of ntype. A pn junction is a device formed by joining ptype doped with b, al with ntype doped with p, as, sb semiconductors and separated by a thin junction is called pn junction diode or. There are two operating regions and three possible biasing conditions for the standard junction diode and these are.
No current thermal equilibrium pn junction at equilibrium 1st step. A diode is a simple device, which can be implemented by a pnjunction, as well as other heterojunction. This allows electrical current to pass through the junction only in. Initiate the pn junction formation by clicking the formjunction button or using mouse drag and watch the physical system approach a new electrothermal equilibrium which is characterized by a constant fermi level throughout the material. Pdf the excerpts presented, from the authors book crystal fire, track the. If ptype semiconductor is joined with ntype semiconductor, a pn junction is formed. Equilibrium band diagrams appear below the semiconductor. We will see what happens when we have a single crystal with a ptype semiconductor on one side and an ntype on the other. Diode allows current to pass in only one direction.
In this type of diode, we dope one side of a semiconductor piece with an acceptor impurity and another side with a donor impurity. 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. A pn junction is the metallurgical boundary between the n and pregions of a semiconductor crystal. 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.
Formation of pnjunction with stable ndoping in graphene field effect transistors using e. A pnjunction is formed when an ntype material is fused together with a ptype material creating a semiconductor diode. A pn junction diode is a twoterminal electronics element, which can be classified as either step graded or linear graded. Pn and metalsemiconductor junctions the gmu ece department. Semiconductor pnjunction diodes physically, diodes are formed by the interface between two regions of oppositely doped semiconductor i. The pn junction is the fundamental building block of the electronic age. Pn junction diode engi 242 elec 222 pn junction diode diode model analysis ideal approximation exact diode specification sheets diode resistance static resistance rd.
This pn junction separates ntype semiconductor from ptype semiconductor fig. A pn junction is a boundary or interface between two types of semiconductor materials, ptype and ntype, inside a single crystal of semiconductor. Smith department of eecs university of california, berkeley eecs 105 spring 2004, lecture 19 prof. In this paper formation a pn junction diode is explained by vlsi fabrication steps which are stated below. A pn junction with open terminals excluding minority carriers f. Silicon a single silicon atom consists of fourteen negatively. 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. Derivation of the ideal pn junction diode equation. Diode is a basic element in electronic and digital circuit. A pn junction is formed by doping a crystal in such a way that the semiconductor changes from p to ntype over a very.
A pn junction is a device formed by combining ptype doped with b,al and n type doped with p,as,sb semiconductors together in close contact. Lecture 15 the pn junction diode i mit opencourseware. Such junctions show a pronounced rectifying behavior. Similarly, holes flow by diffusion from the ptype side to the ntype side. Pn junction theory for semiconductor diodes electronicstutorials. Lets look at how a pn junction is formed and how it behaves under a bias or an externally applied voltage. We will assume, unless stated otherwise, that the doped regions are uniformly doped and that the transition between the two regions is abrupt. Pn junctions are formed by joining ntype and ptype semiconductor materials, as shown below. At the instant of the pn junction formation free electrons near the junction diffuse across the junction into the p region and combine with holes. I have developed a second chapter on the series, which explains the characteristics of pn junction diode.
By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction. The junctions formation mechanism 3 flat fermi level. Cbse ncert notes class 12 physics semiconductor electronics. Questions you should be able to answer by the end of todays lecture. A diode is a 2 lead semiconductor that acts as a one way gate to electron flow. Formation of pn junction in actual practice, a pn junction will not be formed if. Understanding the formation and functioning of a pn junction is paramount to analyzing the working of semiconductor devices.
In this video, lets explore the famous pn junction. 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. Pn junction diode is one of the fundamental elements in electronics. If the electrons and holes were not charged, this diffusion process. 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. The region in which the ptype and ntype semiconductors are joined is called pn junction. This chapter introduces several devices that are formed by joining two different materials together. A voltage results from the electric field formed at the junction. The pn junction has the very useful property that electrons are only able to flow in one direction. The pn junction diode may get destroyed due to excessive heat if any of these values are exceeded.
Ppt pn junction diode powerpoint presentation free to. Because a boron atom has only three electrons available in its bonding shell, only three covalent bonds can be formed between a boron atom and the silicon. From the above, it follows that zero power dissipation occurs in an ideal diode. Most semiconductor devices contains one or more pn junctions. Silicon wafer cleaning rca process in the ic processing wafers it is necessary to maintain the purity and perfection of material. The pn junction provides satisfactory performance when operated within these limiting values. 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. A ptype has a lot of holes and an ntype lot of electrons. Here you may find a good video with animation, which explains the formation of pn junction. If the depletion layer region has a distance d, it therefore must therefore penetrate into the silicon by a distance of dp for the positive side, and a distance of dn for the negative side giving a relationship between the two of. They are also called pn diodes in analogy with vacuum diodes. Frequently we will deal with pn junctions in which one side is. 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 pn junction is of great importance as it is the main control element for the semiconductor devices. Because it gives rise to discontinuities across the crystal structure. Review, pn junctions, fermi levels, forward bias prof j. Special fabrication techniques are adopted to form a p n junction 4.
Semiconductors pn junction theory interview questions and answers pdf free download. On the pside of the junction, 0 0 a mp qn e x on the nside of the junction, 0 0 d mn qn e x at the junction interface. Formation of pnjunction with stable ndoping in graphene. The pn junction is the basis for diodes, certain transistors, solar cells, and other devices. A ptype material consists of silicon atoms and trivalent impurity atoms such as. What is a pn junction when a ptype semiconductor is suitably joined to an ntype semiconductor, the contact surface is called pn junction. The pn junction diode is the basic semiconductor diode format. 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. Convert a part of the ptype semiconductor into ntype silicon semiconductor by adding a small. As we know, if we use different semiconductor materials to make a pn junction, there will be a grain boundary that would inhibit the movement of electrons from one side to the other by scattering the electrons and holes and thus we use the. How a pn junction formed in a diode engineering tutorial. Formation of p n junction forward bias reverse bias p n junction formula. Lots of electrons on the left hand side of the junction want to diffuse to the right and lots of holes on the right hand side of the junction want to move to the left.