The solid circles on the right of the junction represent the available electrons from the ntype dopant. Silicon pn junctions have a higher potential barrier than germanium junctions. Mar 18, 2012 it happens, but not to that extent that all holes and electrons pair up. We can visualize the formation of a pn junction by considering what happens as we bring together two semiconductors, initially separated at 1. As you can see, the valence and conduction bands in the n region are at lower energy levels than those in the p region, but there is a significant amount of overlapping. Forward biasing a pn junction diode is very simple. The pn junction is a versatile element, which can be used as a. This pn junction separates ntype semiconductor from ptype semiconductor fig. What are the depletion width in the nregion, the depletion width in the pregion, and the builtin potential at 300k. A device modeling program is developed using the basic matlab tools necessary to understand the operation of the program and allow future developments as necessary. Shockley model from sze, 1981 vv at 1 j j e tot s n n p p p n s l d n q l d p j 0 0 j j x j x tot n p p n a i n n n d n q 2 w p n. Zero bias no external voltage potential is applied to the pn junction diode.
By definition, ntype semiconductor has an excess of free electrons compared to the ptype region, and. The junctions formation mechanism 3 flat fermi level. A pn junction with open terminals excluding minority carriers f. Explain the formation of depletion layer in pn junction electrons and holes diffuse into regions with lower concentrations of electrons and holes, much as ink diffuses into water until it is uniformly distributed. 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. A pn junction is the metallurgical boundary between the n and pregions of a semiconductor crystal. Forming a junction nd na space charge fixed mobile carriers d n n junction x a p n 2 n0 ni na before joining the p and the n side valid only in equilibrium klimeck ece606 fall 2012 notes adopted from alam forming a junction 10 d n n junction actual carrier concentrations bulk regiondepleted region nside pside n n p p lnn, ln. An abrupt silicon pn junction n a 10 16 cm3 and n d 4 x 10 16 cm3 is biased with v a 0. What is the currentvoltage characteristic for the pn junction diode. Similarly holes near the junction from the p type cross the junction and are filled by the electrons in the ntype. Pdf for the first time, the idea of a twodimensional pn junction formed as a contact between two regions of a quantumdimensional film with. Solid state devices lecture 14 electrostatics of p. Jul 06, 2016 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. The magnitude of the potential barrier is a function of the materials used in manufacturing.
When ptype and ntype materials are placed in contact with each other, the junction behaves very differently than either type of material alone. Your browser needs to be applet enabled in order for you to be able to see the interesting program i provided here. A pn junction is formed by diffusing a ptype material to an ntype wafer and there are several other ways as well, see your text. Pdf formation of pn junction with stable pdoping in. 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. The doping profile is our starting point to analyze pn junction electrostatics, since it combines the information given for n d and n a. The pn junction most semiconductor devices contain.
There is a builtin voltage at the pn junction interface that prevents penetration of electrons into the pside and holes into the nside. When a junction is formed in a silicon wafer by doping, a concentration gradient occurs between ptype and ntype materials. Formation of pn junction along the bilayer channel we now discuss the characteristics of drainsource current i ds as a function of drainsource bias v ds. Semiconductor pn junction diodes physically, diodes are formed by the interface between two regions of oppositely doped semiconductor i. 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. 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 bi by v. How a pn junction formed in a diode engineering tutorial.
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. Formation of pn junction with stable pdoping in graphene field effect transistors using deep uv irradiation article pdf available in journal of materials chemistry 118 february 20. The diffusion forms a dipole charge layer at the pn junction interface. When ptype material is joined with ntype material, something magical happens which makes it one of the most widely used semiconductor device. When a pn junction is formed, some of the free electrons in the nregion diffuse across the junction and combine with holes to form negative ions. Pdf the excerpts presented, from the authors book crystal fire, track the work of an.
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. Convert tiff to pdf, ocr pdf, make a pdf creator v10 megaupload searchable pdfs with high performance ocr pdf software. Formation of a pn junction diode and its band diagram. Pn and metalsemiconductor junctions the gmu ece department. Physics of semiconductor devices pn junction depletion width. This page of application notes section covers pn junction diode applications. Electrons and holes diffuse into regions with lower concentrations of electrons and holes, much as ink diffuses into water until it is uniformly distributed. Pdf twodimensional pn junction under equilibrium conditions. Pn junction underbiasing 14 boltzmanns approximation. If ptype semiconductor is joined with ntype semiconductor, a pn junction is formed. By mouse drag of the rectangles toward each other or clicking on the formthejunction button, you can bring the two bulk semiconductors to form the junction. As shown in the figure, pn junction diode is a 2 terminal polarity sensitive device. The shift of electrons from n side of the pn junction to holes annihilated on the p side of the pn junction produces a potential barrier voltage. The formation of a pn junction in a polymer electrolyte topgated bilayer graphene transistor article pdf available in nanotechnology 2036.
The pn junction is the fundamental building block of the electronic age. Silicon a single silicon atom consists of fourteen negatively. Formation of a pnjunction overview joining ntype material with ptype material causes excess electrons in the ntype material to diffuse to the ptype side and excess holes from the ptype material to diffuse to the ntype side. By definition, ntype semiconductor has an excess of free electrons compared to the ptyp. Semiconductor device characteristics and operation are intimately connected to these pn junctions, therefore considerable attention is devoted initially to this basic device. The main noticeable feature is a clear nonlinear dependence of i. 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. Pn junction one of the crucial keys to solid state electronics is the nature of the pn junction. 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. Changing the way people view, share and work with edocuments. How to calculate it based on fermi levels of semiconductors forming the junction. The formation of a pn junction in a polymer electrolyte.
A ptype material consists of silicon atoms and trivalent impurity. Pn junction tutorial introduction to pn junction diodes. How is a depletion layer formed in a pn junction diode. 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. Electrons near the junction from the ntype materials cross the junction and fill up some holes in the p type materials. Pn junctions are formed by joining ntype and ptype semiconductor materials, as shown below.
Therefore, a diffusion currentflows across the junction from each side. A click on a button will show an animated formation of pn junction diode, a snapshot of which is. The physical point at which the ntype and ptype semiconductors merge is referred to as the. An energy diagram for a pn junction at the instant of formation is shown in figure a. Physics of semiconductor devices pn junction depletion width problem a silicon pn diode has a doping of n d 81015 1 cm3 and n a 210 16 1 cm3. Here you may find a good video with animation, which explains the formation of pn junction. The upward direction in the diagram represents increasing electron energy. This pn diode applications are very useful for beginners. I have developed a second chapter on the series, which explains the characteristics of pn junction diode. Near the junction, electrons diffuse across to combine with holes, creating a depletion region. A voltage results from the electric field formed at the junction. A pn junction is a sandwiched semiconductor structure consisting of an ntype semiconductor and. Filling a hole makes a negative ion and leaves behind a positive ion on the n side.
Figures 3a and b show i ds versus v ds for different topgate voltages. Id decreases in equilibrium, there is a v r across the terminals greater than v 0 if i is, the diode breaks down. This applet demonstrates how the band diagram of a pn junction diode is formed. It happens, but not to that extent that all holes and electrons pair up. The region in which the ptype and ntype semiconductors are joined is called pn junction. A pnjunction is formed when an ntype material is fused together with a ptype. The pn junction is the basis for diodes, certain transistors, solar cells, and other devices. 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. Pn junction diode applications pn diode applications. The pn junction diode provides characteristics that.
Pn junction theory for semiconductor diodes electronicstutorials. Physics of semiconductor devices pn junction depletion. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction. Diode is formed simply by joining ptype and ntype semiconductor material, nothing more. 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. Formation of pn junction 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 process of doping. Shockley model from sze, 1981 vv at 1 j j e tot s n n p p p n s l d n q l d p j 0 0 j j x j x. The energy level sketch above right is a way to visualize the equilibrium condition of the pn junction. The dopants are assumed to be shallow, so that the electron hole density in the n type p type region is. This chapter introduces several devices that are formed by joining two different materials together. In the simpler case of a very highly asymmetric junction for example. The formation of a pn junction in a polymer electrolyte top. They are also called pn diodes in analogy with vacuum diodes.
Solid state devices lecture 14 electrostatics of pn. Pn junctions consist of two semiconductor regions of opposite type. 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. The red rectangle represents a ptype semiconductor and the blue rectangle an ntype semiconductor. The formation of the junction and potential barrier happens during the manufacturing process. The region on the left is p type with an acceptor density na, while the region on the right is n type with a donor density nd. Pn junction in equilibrium no bias applied because each side of the junction contains an excess of holes or electrons compared to the other side, there exists a large concentration gradient.
It will help you to grasp concepts behind pn junction even better. To return the semiconductor to separate pieces, click the separate button or drag one object away from th. To merge pdfs or just to add a page to a pdf you usually have to buy expensive software. Specifically, current will flow readily in one direction forward biased but not in the other reverse biased, creating the basic diode. Our servers in the cloud will handle the pdf creation for you once you have combined your files. In order to initiate the junction formation, click the formjunction button or mouse drag one object toward the other. Pn junction diode junction diode symbol and static iv characteristics. A ptype material consists of silicon atoms and trivalent impurity atoms such as. Thanks to tiff junction, i was able to convert over 900 files in less than 30 minutes total and i had. A pn junction is one formed between two semiconductors with different. From the above, it follows that zero power dissipation occurs in an ideal diode. Negligible scl generation and recombination relate minority populations at qnr edges, x p and x n, to v ab use nx p, px n to find hole and electron. Majority carriers in quasiequilibrium with barrier 4. In a ptype semiconductor, majority carriers are holes or positive charges.
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