Semiconductor pn junction diode is the simplest semiconductor device. Pn junction properties calculator select a semiconductor substrate and a doping profile below. 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. This is called the depletion region or the space charge layer. Depletion capacitance university of california, berkeley. As a positive voltage is applied, the potential across the semiconductor decreases and with it the depletion layer width. A pn junction at equilibrium is characterized by a depletion region where.
Diode theory pn junction, biasing, characteristic curves. The term junction refers to the boundary interface where the two regions of the semiconductor meet. Pn junction diode 12 spice model for pn junction diode r s. Any variation of the charge within a pn diode with an applied voltage variation yields a capacitance wich must be added to the circuit model of a pn diode. As it is lightly doped, it will add significant ohmic resistance to the diode when it is forward biased. Width of depletion region physics and radioelectronics. By definition, ntype semiconductor has an excess of free electrons compared to the ptyp.
The forerunner to the solid state pn junction is the vacuum tube diode, shown in figure. A pn junction is the metallurgical boundary between the n and pregions of a semiconductor crystal. When p n junction is formed a depletion layer is formed on either side of the junction. The pn junction is one of the primary building blocks of semiconductors. Mobile electrons of pside of the pn junction diode constitute. The p region has many holes majority carriers from the.
Ee105 fall 2014 microelectronic devices and circuits. Thus, the depletion layer insulator is widened and no current flows through the pn junction. As a result there is the formation of junction between the two semiconductors called pn junction. Also called transition region capacitance or depletion layer capacitance. Here dopants means outsiders, pn junction diode means a v. The pn junction is a versatile element, which can be used as a. This process of diffusion continues until and unless a sufficient number of impurity ions in the form of donor and acceptor impurity are uncovered and a potential difference of nearly 0. The electrons which had migrated across from the n to the p region in the forming of the depletion layer have now reached equilibrium. A region depleted of mobile charge carriers exists in the vicinity of the metallurgical. A negative charge is established on the p side of the junction. The depletion layer width, built in voltage, maximum field, and depletion capacitance will be displayed in the appropriate boxes. The behavior of the pn junction with regards to the potential barriers width produces an asymmetrical conducting two terminal device, better known as the pn junction diode. Feb 16, 2019 in this physics video in hindi we explained the working of a pn junction diode for class 12. The depletion layer width, builtin voltage, maximum field, and depletion capacitance will be displayed in the appropriate boxes.
The behaviour of the pn junction with regards to the potential barriers width produces an asymmetrical conducting two terminal device, better known as the pn junction diode. One terminal of pn junction diode is anode and other is cathode. Pn junction diode in the reversebiased configuration is sensitive to light from a range between 400nm to nm, which includes visible light. As the depletion layer built up a different of potential appears across the junction this difference of potential at junction is called potential barrier. The capacitance at the depletion region changes with the change in applied voltage. Physics of semiconductor devices pn junction depletion. Energy band diagram of a pn junction under reverse and forward bias pn juntion diode. The depletion width shrinks in forward bias and expands in reverse bias. What happens when we join ptype and ntype semiconductors. 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. Pn junctions consist of two semiconductor regions of opposite type. 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. The point at which this sudden increase in current.
Abrupt depletion layer approximation let apply bias and calculate current through the pn junction currents in pn junction from sze, 1981. When we connect ptype region of a junction with the positive terminal of a voltage source and ntype region with the negative terminal of the voltage source, then the junction is said to be forward biased. Thickness of depletion layer in pn junction stack exchange. Gilbert ece 340 lecture 27 102912 junction capacitance basically, there are two types of capacitance associated with a pn junction the first is junction capacitance. We also explained how depletion region is created, what barrier potential is and what diffusion.
At this condition, due to the attraction of positive terminal of source, electrons which participated in covalent bond creations in ptype material, will be. The regions near the pn interface lose their neutrality and most of their mobile carriers, forming the space charge region or depletion layer see figure a. Pn junction diode multiple choice questions answers. Electrostatics of pn junction in equilibrium a spacecharge region surrounded by two quasineutral regions formed. If we apply a external field across the diode forward bias of the opposite polarity of the internal diode junction field it will be neutralized to zero as the external potential is increased and the depletion zone will shrink in size to almost nothing. Silicon a single silicon atom consists of fourteen negatively. Specifically, current will flow readily in one direction forward biased but not in the other reverse biased, creating the basic diode.
Lecture 5 pn junction and mos electrostatics ii pn junction in thermal equilibrium september 22, 2005 contents. Such junctions show a pronounced rectifying behavior. Diode junction capacitance transition capacitance and. Electrons and holes diffuse into regions with lower concentrations of electrons and holes, much as ink diffuses into water until it is uniformly distributed. Formation of depletion layer, barrier voltage and biasing in. The n drift region is absent in low power signal diodes. Explain the formation of potential barrier and depletion layer. The current in the pn junction diode can only flow from one side to the other. The forward bias decreases the resistance of the diode whereas the reversed bias increases the resistance of the diode. When a pregion of a semiconductor diode is connected with the positive terminal of battery and the nregion with negative terminal of the battery then the pn.
The only elements left in the depletion region are ionized donor. What are the depletion width in the nregion, the depletion width in the pregion, and the built in potential at 300k. Any semiconductor junction will contain a depletion region of nonconducting semiconductor between the two conducting regions. Led or a laser diode r ohms v9v va i v 1ir light emission under forward bias diode made from a direct bandgap semiconductor. Coulomb force from ions prevents further migration across the pn junction. Pn junction diode and its characteristics in chapter 1 understanding the pn junction, we have seen how a pn junction is formed from a ptype and ntype semiconductor. Electrostatics of pn junction in thermal equilibrium 3. Majority carriers that are injected to the opposite side. Apr 23, 2018 semiconductor pn junction diode is the simplest semiconductor device. Sep 23, 2017 simplest way as my professor taught for easy understanding when outsiders comes to live in a village then amount of agricultural field is automatically reduced for the native villagers. 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. 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.
The hetero pn junction the heterojunction n diode is in principle very similar to a homojunction. A pn junction is a junction formed by joining ptype and ntype semiconductors together in very close contact. Understanding pn junction is essential to understanding transistor operation. A depletion region is a natural feature of doping a semiconductor ntype and right next to it ptype. The result is a region near the junction that acts to repel the mobile charges away from the junction through the electric field that these charged regions create. Physics of semiconductor devices pn junction depletion width. Depletion layer opposes only the the majority carrier not minority carrier. The reverse biased pn junction negative electrons in the ntype feel an attractive force which pulls them away from the depletion layer positive holes in the ptype also experience an attractive force which pulls them away from the depletion layer. The depletion region acts like a wall between ptype and ntype semiconductor and prevents further flow of free electrons and holes. The application of a forward biasing voltage on the junction diode results in the depletion layer becoming very thin and narrow which represents a low impedance path through the junction thereby allowing high currents to flow.
The total charge on each side of a pn junction must be equal and opposite to maintain a neutral charge condition around the junction. Biased pn junction when a positive voltage is appliedon p side, the equilibrium is destroyed and a net current can flow 9 simplifyingassumptions. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction. Nonideal pn junction diodes engineering libretexts. What are the depletion width in the nregion, the depletion width in the pregion, and the builtin potential at 300k. From xxnnpn da00 under reverse bias, vbi has to be replaced with vbivr.
It acts like a dielectric non conductive between p and n regions. P n junction theory and diodes part i gate problems. We have also learned about diffusion current, depletion region. Aug 10, 2015 the effect of adding this additional energy source results in the free electrons being able to cross the depletion region from one side to the other. Capacitor c includes depletion layer capacitance for the reversebias region and diffusion capacitance associated with the junction under forward bias. Junction breakdown reverse bias energy band diagram.
Pn junction diode and its symbol formation of depletion layer barrier voltage biasing of pn junction diode 1. In semiconductor physics, the depletion region, also called depletion layer, depletion zone. For example, a common type of transistor, the bipolar junction transistor, consists of two pn junctions in series, in the form npn or pnp. 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.
This recombination of electrons and holes produces a narrow region at junction called depletion layer. 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. 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. Formation of depletion layer, barrier voltage and biasing. When reverse bias voltage applied to the pn junction diode is increased, a large number of holes majority carriers from pside and electrons majority carriers from nside are moved away from the pn junction. 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. For higher breakdown voltages, the drift region is wide. How is a depletion layer formed in a pn junction diode. P n junction theory and diodes part i gate problems 1. Electrons are continuously vibrating and the electrons of ntype material near the ptype material will be attracted towards that, they will move to fill up the holes present near the junction of ptype semiconductor. The pn junction is the fundamental building block of the electronic age. Pn junction one of the crucial keys to solid state electronics is the nature of the pn junction. P and n regions have low resistance, so they act like two plates of a. A schottky junction is a special case of a pn junction, where metal serves the role of the ptype semiconductor.
Depletion region created across the pn junction by the initial movement of majority carrier across the junction. The total potential across the semiconductor equals the built in potential minus the applied voltage, or. To solve the problem, the free carrier, p and n, must be taken into account during calculations. Within the depletion region, there are very few mobile electrons and holes.
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. Why does a depletion region in a pn junction decrease with. These devices may not be a simple pn type diode, but behave electrically identical to a pn junction diode. Note the depletion layer is the region around the junction in which the free charge carriers are depleted. The capacitance associated with the charge variation in the depletion layer is called the junction capacitance, while the capacitance associated with the excess carriers in the quasi. In this case the charge densities in the space charge region are. This allows the charge carriers to pass thru the junction easily. In this video we are going to learn the following topics. 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. Degradation of forward current density with increasing. If a reverse voltage exceeds this level, the voltage will punch through the depletion layer and allow current to. They are also called pn diodes in analogy with vacuum diodes. Because of the structure of a semiconductor junction, the effective width of this depletion layer is not constant. An ideal pn junction diode is based on the following basic assumption.
Space charge region an overview sciencedirect topics. Diodes and thyristors a diode one way valve is a pn junction with ptype on one side and ntype on the other. Other electrons from the n region cannot migrate because they are repelled by the negative ions in the p. The result is that a high potential barrier is created thus preventing current from flowing through the semiconductor material. No generationrecombination in the depletion layer 6. Questions you should be able to answer by the end of todays lecture. The depletion layer of the diode is very thin in forward biasing and thick in reverse bias. When ptype and ntype materials are placed in contact with each other, the junction behaves very differently than either type of material alone. The depletion region is also called as depletion zone, depletion layer, space charge region, or space charge layer. Aug 08, 2018 in this video we are going to learn the following topics. 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. Low injection fermi level do not change in the depletion layer. Semiconductor pn junction diode working pn diode vi.
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