A pn junction is a boundary or interface between two types of semiconductor materials, ptype and ntype, inside a single crystal of semiconductor. Apr 05, 2019 the current that flows in a pn junction diode is the small leakage current, due to minority carriers generated at the depletion layer or minority carriers which drift across the 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. This pn junction separates ntype semiconductor from ptype semiconductor fig. It becomes nonconductive intrinsic semiconductor material. Pn junction tutorial introduction to pn junction diodes. The current that flows in a pn junction diode is the small leakage current, due to minority carriers generated at the depletion layer or minority carriers which drift across the pn junction. In a pn junction depletion region is developed when electrons from nregion diffuse to pregion and hole from pregion diffuse to nregion. Pnjunction diode and diode circuits 1 main properties of semiconductors 2 the pnjunction in equilibrium 3 the i v characteristics of the pnjunction 4 deviations from the ideal diode 5 analysis of the diode circuits 6 rectifier circuits. The applied voltage determines the amount of charge stored in the junction. 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.
The depletion width shrinks in forward bias and expands in reverse bias. The pnjunction is the root for semiconductor diodes. Near the junction, electrons diffuse across to combine with holes, creating a depletion region. The process of diffusion takes place due to which the majority carriers diffuse from one region to the other so the pregion becomes less positive and. Electrical engineering stack exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. The term junction refers to the boundary interface where the two regions of the semiconductor meet. Pn junction diode and its symbol formation of depletion layer barrier voltage biasing of pn junction diode 1. Apr 01, 20 how depletion layer or potential barrier is formed in the pn junction diode in a pn junction diode holes are the majority carriers on p side whereas electrons are the majority carriers on nside. A pn junction with open terminals excluding minority carriers f. This width will vary for a silicon diode and a germanium diode. This depletion region has a predefined width, say w. What are the depletion width in the nregion, the depletion width in the pregion, and the builtin potential at 300k.
Finally, the result is that the growth in the width of the depletion layer presents a high impedance path which acts as an insulator. As the diffusion current increases, holes from the pside diffuse to the nside and electrons from the nside diffuse to the pside which gives rise. Since a junction forms between a p type and n type material it is called as pn junction. What are the leading dependences of the smallsignal elements. This allows electrical current to pass through the junction only in. A silicon pn junction is forward biased with a constant current at room temperature. Working of pn junction diode with biasing, characteristics. Dec 03, 2003 if the depletion region width shrinks as temperature increases its because the density of carriers is increasing. 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. Width of depletion region physics and radioelectronics.
The region in which the ptype and ntype semiconductors are joined is called pn junction. Thus, pn junction diode can be considered as a parallel plate capacitor. Depletion capacitance university of california, berkeley. The other differences between the pnjunction and zener diode are shown in the comparison chart. In the depletion layer all the atoms are complete and have no free electrons left within. Finally, the result is that the growth in the width of the depletion layer presents 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. Physics of semiconductor devices pn junction depletion. When the pn junction is formed a electric field is created by the movement of electrons and holes to equalize in equilibrium the device is overall neutral the charge across the junction. In this video we are going to learn the following topics. This recombination of electrons and holes produces a narrow region at junction called depletion layer. When a pregion of a semiconductor diode is connected with the positive terminal of. The pn junction has the very useful property that electrons are only able to flow in one direction. How depletion layer or potential barrier is formed in the pn. Depletion region shrinks with increased temperature. The stored charge in the depletion region, however, unlike the case of a parallel plate capacitor, does not depend linearly on the voltage.
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. The analysis is very similar to that of a metalsemiconductor junction section 3. Vi characteristics of pn junction diode in 3biasing modes. Forward biasing a pn junction diode is very simple. As a positive voltage is applied, the potential across the semiconductor decreases and with it the depletion layer width. Physics of semiconductor devices pn junction depletion width. At reverse bias voltages, only the depletion layer capacitance is present and it is frequency.
It is the most essential and the basic building block of the electronic device. By applying a negative voltage reverse bias results in the free charges being pulled away from the junction resulting in the depletion layer width being increased. And the zener diode is heavily doped and has thin depletion which makes their. Energy band diagram of a pn junction under reverse and forward bias pnjuntiondiode. Step junction solution bi a a d s o a d p n bi a a a d s o d bi a p d a d s o a n v v n n n n q k w x x v v n n n n q k v v and x n n n n q k x. The energy level sketch above right is a way to visualize the equilibrium condition of the pn junction. If ptype semiconductor is joined with ntype semiconductor, a pn junction is formed. The total potential across the semiconductor equals the builtin potential minus the applied voltage, or. The only elements left in the depletion region are ionized donor. The pn junction is lightly doped and having large depletion region which is only eliminated by forward biasing. How depletion layer or potential barrier is formed in the pn junction diode in a pn junction diode holes are the majority carriers on p side whereas electrons are the majority carriers on nside. Hence, the depletion region acts like the dielectric or insulating material.
The word diode can be explained as di means two and ode is obtained from electrode. A pn junction at equilibrium is characterized by a depletion region where. The pn junction is the fundamental building block of the electronic age. The energy band information is summarized in figure 10. In addition to the junction capacitance, are there any other capacitive e. From cv characteristics, we deduce a linearly graded junction nature and a builtin value of. The total potential across the semiconductor equals the built in potential minus the applied voltage, or. The pn junction is the root for semiconductor diodes. If the diode is connected in reverse bias holes are extracted from the ptype region and free electrons from the ntype region and so the depletion layer widens. The region in the vicinity of the junction, which has been depleted of the free charge. Depletion region shrinks with increased temperature physics. 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. The depletion region of the pn junction diode has high resistance. Pn junction diode multiple choice questions answers.
When the diode is forwardbiased, it can be used in led lighting applications. The process by which a depletion region at the pn junction is destroyed and allows a large reverse current is called depletion region breakdown in reverse biased pn junction diode, the negative terminal of the battery is connected to the ptype semiconductor whereas the positive terminal of the battery is connected to the ntype semiconductor. 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. Depletion region formation in pn junction diode and potential barrier shahab yousafzai december 9, 2018 electronics engineering no comments pn junction diodes are made by doping the trivalent element into one side of an intrinsic semiconductor like silicon and doping pentavalent to another side of it. The width of depletion region is depends on the amount of impurities added to the semiconductor. Depletion region breakdown physics and radioelectronics. As the depletion layer built up a different of potential appears across the junction this difference of potential at junction is called potential barrier. In case of the schottky diode solar cell and assuming ntype semiconductor, one can choose a metal such that its phi1 is equal to that of the p. Forward biasing reduces the barrier potential the voltage applied is in a sense which is opposite to that due to the space charge regions within the pn junction around the depletion regio which facilitates an increase in the diffusion current. Capacitor c includes depletion layer capacitance for the reversebias region and diffusion capacitance associated with the junction under forward bias. Schottky diode has a metal and ntype semiconductors junction. Additional defect information has also been gained from other well known. They are differentiated by their property of current conduction. Pn junction one of the crucial keys to solid state electronics is the nature of the pn junction.
I in forward bias, negligible in reverse bias junction capacitance. Silicon a single silicon atom consists of fourteen negatively. An electronic device that restricts current flow chiefly to one direction. How depletion layer or potential barrier is formed in the. Here diffusion thereby development of depletion is caused by the movement of majority carriers. This condition represents the low resistance path through the pn junction allowing very large currents to flow through the diode with only a small increase in bias voltage. The fulldepletion approximation assumes that the depletion region around the metallurgical junction has welldefined edges with an abrupt transition between the fully depleted region where no carriers are present and the quasineutral region, a neutral region where the carrier density is close to the doping density. Depletion region formation in pn junction diode and. When ptype and ntype materials are placed in contact with each other, the junction behaves very differently than either type of material alone.
Diode is formed simply by joining ptype and ntype semiconductor material, nothing more. In semiconductor physics, the depletion region, also called depletion layer, depletion zone, junction region, space charge region or space charge layer, is an insulating region within a conductive, doped semiconductor material where the mobile charge carriers have been diffused away, or have been forced away by an electric field. A pn junction is a junction formed by joining ptype and ntype semiconductors together in very close contact. The pn junction diode is the basic semiconductor diode format. 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. Pn junction diode baising and its vi characteristics. Special pages permanent link page information wikidata item cite this page. This region of positive charge and negative charge on either side of the junction is termed as the depletion region. If the depletion region width shrinks as temperature increases its because the density of carriers is increasing. It is apparent that the depletion region of a pn junction has positive and negative charges separated over a distance w similar to a parallel plate capacitor. If the voltage applied on the pn junction diode is increased to a higher value, a very strong electric field is built in this narrow depletion region. Pdf defect analysis in semiconductor materials based on pn. Since no free charge carriers can rest in a position where there is a potential barrier, the regions on either sides of the junction now become completely depleted of. As the diffusion current increases, holes from the pside diffuse to the nside and electrons from.
This strong electric field of narrow depletion region applies force on the valence electrons and pulls them from the valence band. This pn junction separates ntype semiconductor from ptype semiconductor. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction. The solid circles on the right of the junction represent the available electrons from the ntype dopant. The full depletion approximation assumes that the depletion region around the metallurgical junction has welldefined edges with an abrupt transition between the fully depleted region where no carriers are present and the quasineutral region, a neutral region where the carrier density is close to the doping density.
Hence, ptype and ntype regions act like the electrodes or conducting plates of the capacitor. Now, if we join the two types of semiconductors ptype and ntype together then a new device is formed called as pn junction diode. In semiconductor physics, the depletion region, also called depletion layer, depletion zone. The actual potential difference across the junction or diode is kept constant by the action of the depletion layer at approximately 0. Explain the formation of potential barrier and depletion layer. It is also required to obtain the capacitancevoltage characteristics of the diode. The pn junction diode and the zener diode both are made up of semiconductor material. Ee105 fall 2014 microelectronic devices and circuits. The energy level sketch above right is a way to visualize the. At the junction, majority carriers diffuse across the junction, and this creates a depletion layer and a barrier potential v barrier across the junction. The pn junction solidstate device theory electronics.
Pn junction diode and diode characteristics electronicstutorials. Pn junction diode 12 spice model for pn junction diode r s. Formation of depletion layer, barrier voltage and biasing. Capacitor c includes depletionlayer capacitance for the reversebias region and diffusion capacitance associated with the junction under forward bias. In effect, we have nearly an insulator separating the conductive p and n doped regions. The mobile carriers are further inhibited from crossing the junction. Thus a reverse biased pn junction does not conduct current 15. A is the crosssectional area of the pn junction xp is the distance. Introduction to semiconductors and the pn junction diode.
This creates the depletion zone where no free charge carriers are available to allow for current flow. 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. Specifically, current will flow readily in one direction forward biased but not in the other reverse biased, creating the basic diode. What are the depletion width in the nregion, the depletion width in the pregion, and the built in potential at 300k. The electrostatic analysis of a pn diode is of interest since it provides knowledge about the charge density and the electric field in the depletion region. The thin layer of the crystal lattice between these charges has been depleted of majority carriers, thus, is known as the depletion region. By definition, ntype semiconductor has an excess of free electrons compared to the ptyp. How is a depletion layer formed in a pn junction diode. What is the currentvoltage characteristic for the pn junction diode.
Pn junction theory for semiconductor diodes electronicstutorials. Pnjunction diode characteristics ppt documentation. The voltage v barrier causes an opposing current flow, and the two flows form an equilibrium. Energy band diagram of a pn junction under reverse and forward bias pn juntion diode. Movement of electrons and holes when forming the junction depletion region approximation. Depletion region is a region near the pn junction where flow of charge carriers free electrons and holes is reduced over a given period and finally results in zero charge carriers. Additional defect information has also been gained from other wellknown. Typically at room temperature the voltage across the depletion layer for silicon is about 0. Pn junction diode in the reversebiased configuration is sensitive to light from a range between 400nm to nm, which includes visible light.
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