However, after 1990, a few semiconductor devices using organic semiconductors and semiconducting polymers have been developed signalling the birth of a futuristic technology of polymerelectronics and molecularelectronics. Smith department of eecs university of california, berkeley eecs 105 spring 2004, lecture 19 prof. Schematic energy band representations of a an insulator, b a semiconductor, and c conductors. There are plenty of electrons in the ntype material and plenty of holes in the ptype material. And on the flip side nni2p is a ptype material because pnand. Ptype, ntype semiconductors engineering libretexts. Similarly, in a ptype semiconductor, with nd 0, we have na. One impurity atom is added to 10 million atoms of an intrinsic semiconductor. In this chapter, we will restrict ourselves to the study of inorganic semiconductors, particularly. The term junction refers to the boundary interface where the two regions of the semiconductor meet. In ntype semiconductors, electrons are the majority carriers and holes are the minority carriers.
Multimedia from the physical chemistry book shows how the energy gap of silicon can lead to. The region where the ptype and ntype semiconductors are joined is called pn junction. A common dopant for ntype silicon is phosphorus or arsenic. Types of doped semiconductors there are two different ways of adding an impurity to the semiconductor atom. Because the fermi level is exactly what doping alters. When the trivalent impurity is added to an intrinsic or pure semiconductor silicon or germanium, then it is said to be an ptype semiconductor. When the applied voltage is lower than the builtin voltage, the current is still nearly zero ptype ntype when the voltage exceeds the builtin voltage, the current can flow through. When ptype and type semiconductors are brought together, electrons move. In this article, you will find the study notes on semiconductors1 which will cover the topics such as introduction, semiconductor materials, intrinsic and extrinsic semiconductors, properties of semiconductor materials and important terms. In the similar way, when an ntype semiconductor is joined with the ptype semiconductor, a pn junction is formed. The doping of semiconductors georgia state university.
Forming a pn junction doping one side of a piece of silicon with boron a ptype dopant and the other side with phosphorus an ntype dopant forms a pn junction. Silicon is an important semiconductor for which n 1. During the formation of pn junction, and due to the concentration gradient across p, and n sides, holes diffuse from pside to nside p n and electrons diffuse from nside to pside n p. It is the branch of physics that deals with the emission and effects of electrons emission and. Na and nd are acceptor and donor atoms respectively. In most cases, the doping of a semiconductor leads either to the creation of donor or acceptor levels ntype ptype semiconductors. Difference between p type and n type semiconductor. The concentration of holes in the ntype semiconductor is obtained by substituting eqn. By introducing group v elements like phosphorous into silicon, extra valence electrons. The hetero pn junction the heterojunction n diode is in principle very similar to a homojunction. The term ntype indicates that the charge carriers are the negativelycharged electrons.
The various factors like doping element, nature of doping element, the majority and minority carriers in the ptype and ntype semiconductor. Similarly, in a ptype semiconductor, the concentration of holes is mor e than the concentration of electrons. The total of eight electrons can not easily be jiggled out of place by an incoming current. The new element either introduces donor atoms or acceptor atoms. N and ptype semiconductors neither pure siliconsi nor germaniumge are great conductors. They form a crystal lattice by having each atom share all of its 4 valence electrons with neighbouring atoms. I believe its because it is a concentration pni2n so if n goes up p goes down and the material is ntype because nndna. The doping of semiconductors the addition of a small percentage of foreign atoms in the regular crystal lattice of silicon or germanium produces dramatic changes in their electrical properties, producing ntype and ptype semiconductors pentavalent impurities impurity atoms with 5 valence electrons produce ntype semiconductors by contributing extra electrons. When ptype and ntype materials are placed in contact with each other, the junction behaves very differently than either type of material alone. As illustrated in figure 117, each pentavalent atom antimony, in this case forms co valent bonds with four adjacent silicon atoms. The formation of a pn semiconductor junction is described and its conduction properties are discussed. Ntype and ptype semiconductors class 12 notes edurev.
In a ptype semiconductor, the iii group element of the periodic table is added as a doping element, whereas in ntype the v group element is the doping element. Extrinsic semiconductors can be further classified into two types i. Ntype semiconductors are created by doping an intrinsic semiconductor with an electron donor element during manufacture. Ntype material diodes n region has lots of free electrons p region has lots of holes at equilibrium. The main problemp that needs to be tackled is he effect of the bandgap discontinuities and the different materialt parameters, which make the actual calculations more complex even though the n diode p concepts need almost no changing. It is formed when the pentavalent impurity is added to an intrinsic. An ntype semiconductor is produced by adding a donor impurity such as arsenic. Trivalent impurities such as boron b, gallium ga, indium in, aluminium al etc are called acceptor impurity. Ntype silicon, b, a group iii element, introduces holes and creates ptype silicon. Materials, devices and simple circuits download ncert solutions for class 12 physics link of pdf file is given below at the end of the questions list in this pdf file you can see answers of following questions. Semiconductors have lower egs than insulators and can be doped. However, if dope 10 15 n d into the material, then n10 15 and p10 5.
There are a lot of carriers available to cross the junction. Region of transition between n and p type material explanation of np semiconductor. After increasing t by 60c, n remains the same at 1015 cm3 while p increases by about a factor of 2300 because. In a ptype boron doped silicon crystal the corresponding holes will become equally distributed throughout the ptype crystals volume. A pn junction is a boundary or interface between two types of semiconductor materials, ptype and ntype, inside a single crystal of semiconductor. The forward bias on the emitter np junction allows the emitter to conduct freely, in either direc. Ntype semiconductor when pentavalent impurity is added to an intrinsic or pure semiconductor silicon or germanium, then it is said to be an ntype semiconductor. Semiconductor type intrinsic extrinsic ptype ntype. Thus pn n2 i nd 5 where pn is the concentration of holes in the ntype semiconductor. Specifically, current will flow readily in one direction forward biased but not in the other reverse biased, creating the basic diode.
Np semiconductor article about np semiconductor by the. In all cases, np n i2 from principles of electronic materials and devices, second edition, s. Extrinsic semiconductors are made by introducing di. Hence, in ntype semiconductor, free electrons are the majority charge carriers and holes are the minority charge carriers in an extrinsic therefore, known as ntype semiconductors. Trivalent impurity like aluminium, gallium and indium is added in the ptype semiconductor, while in ntype semiconductor pentavalent impurity like arsenic, antimony, phosphorus, bismuth, etc. Because electrons under ordinary conditions will flow in only one direction through such barriers, pn junctions form the basis for creating electronic rectifiers and switches. Review, pn junctions, fermi levels, forward bias prof j. Semiconductor and simple circuitsnot to be republished. The density of electrons and holes, energy level and fermi level, the direction of movement of majority carriers, etc. E is th e electro n co n cen tratio n in th e co n d u ctio n b an d. Similarly, holes are the majority carriers in a semiconductor doped with acceptors and it is termed p type. Mobile charge carriers in semiconductors crystal structures, bonding mobile holes and electrons dopants and doping silicon in thermal equilibrium generationrecombination.
Questions you should be able to answer by the end of todays lecture. Introduction to 1 semiconductors chapter outline 11 the atom 12 materials used in electronic devices current in semiconductors 14 ntype and ptype semiconductors 15 the pn junction chapter objectives describe the structure of an atom discuss insulators, conductors, and semiconductors and how they differ describe how current is produced in a. Ptype semiconductor simple english wikipedia, the free. 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. This allows electrical current to pass through the junction only. For silicon, we can use phosphorus p, arsenic as or antimony sb as donors. On the basis of electrical conductivity, the materials can be divided into three categories. Formation of energy bands as a diamond lattice crystal by bringing together isolated silicon atoms. Pentavalent impurities such as phosphorus, arsenic, antimony etc are called donor impurity. If they were constructed of two separate pieces this would introduce a grain boundary, so pn. The electron in an ntype semiconductor is called the majority carrier, whereas the hole in ntype semiconductor is termed the minority carrier. May 09, 2020 ntype and ptype semiconductors class 12 notes edurev is made by best teachers of class 12.
The term ntype comes from the negative charge of the electron. Semiconductors what are semiconductors p type ntype semiconductors video tutorial duration. Four of the antimony atoms valence elec trons are used to form the covalent bonds with silicon atoms, leaving one extra electron. Ntype and ptype semiconductors electronicselectrical. If both types of dopants are present, the one present in higher concentration determines the type of the semiconductor. Notes for semiconductors chapter of class 12 physics. If the product of the concentrations doesnt change based on what the fermi level is, then the mass action law doesnt care how you dope it. Ntype semiconductors are created on doping a semiconductor by exposing them to other elements. Energy band diagrams for a intrinsic b ntype and c ptype semiconductors. For an insulator at ordinary temperatures, nis much smaller and has a typical value n 107 per m3.
The types of doped semiconductors formed after the addition of the impurity are. A barrier forms along the boundary between ptype and ntype semiconductors that is known as a pn junction. Fifth electron is superfluous, becomes free electron and enters into conduction band. A pn junction is a junction formed by joining ptype and ntype semiconductors together in very close contact.
Conversely, in a ptype semiconductor, holes are majority carriers and electrons are minority carriers. The dopant atoms added to the semiconductor crystal in this case are donor atoms. What is the hole concentration in an n type semiconductor with 1015 cm3 of donors. It is also defined as the boundary between ptype and ntype semiconductor. This document is highly rated by class 12 students and has been viewed 2668 times.
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