Working of pn junction diode with biasing, characteristics. This quick video will give you a complete analysis of energy band diagram of pn juction diode. Energy band diagram an overview sciencedirect topics. Background semiconductors, pn junction diode, forward and reverse biasing, band gap. This type of breakdown diode has a depletion region that is deliberately made narrower than the depletion region in the normal pnjunction diode, but thicker than. The inner workings of a light emitting diode, showing circuit top and band diagram when a bias voltage is applied bottom. They are also called pn diodes in analogy with vacuum diodes. Most semiconductor devices involve regions with two different kinds of doping, so a pnjunction is present in all of them.
A steadystate balance of carriers is achieved at the junction where diffusive flux of the carriers is balanced by the drift flux. The vacuum level is defined as the energy level of electrons that are outside the material. The two semiconductors are not necessarily the same, e. The energy band information is summarized in figure 10.
Physics stack exchange is a question and answer site for active researchers, academics and students of physics. The valence band and conduction band in ntype material are slightly lower than that of ptype material. Most semiconductor devices involve regions with two different kinds of doping, so a pn junction is present in all of them. 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 pn junction biasing the pn junction the diode trouble shooting. E v to be positive if e v,n pn junction theory and applications 4 band diagram showing the location of the carrier at zero bias voltage equilibrium condition. Formation of a pn junction diode and its band diagram. May 05, 2018 in this video, i go over the band diagram of the pn junction, which will allow us to find the electric field and the pn junction width through what is called the builtin potential vbi. Lets get a voltmeter and ammeter and connect it to the forward biased circuit of pn junction diode. A diode is a simple device, which can be implemented by a pn junction, as well as other hetero junction structures. The normal ideal diffusion current exists in the device. Electrons in the two bits have different electrochemical potentials i. It is also called as esaki diode named after leo esaki, who in 1973 received the nobel prize in physics for discovering the electron tunneling effect used in these diodes.
A diode is a simple device, which can be implemented by a pnjunction, as well as other. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction. Therefore, a drift current and a diffusion current is flowing. The depletion region extends mainly into the pside. Define parameters that determine solar cell efficiency. Tunnel diode definition, symbol, and working diode. E g1 and e g2 are the band gap energies of the two semiconductors and e f is the fermi level. In silicon, the bonding energy of the covalent bond is 1. Silicon a single silicon atom consists of fourteen negatively. Band diagram of a heterojunction pn diode under flatband conditions the flatband energy band diagram of a heterojunction pn diode is shown in the figure below. Oct 05, 2017 in this lecture, i discussed about the energy band diagram of the pn junction in equilibrium. It acts as a diode, which can serve in electronics as a rectifier, logic gate, voltage regulator zener diode, switching or tuner varactor diode. The solid circles on the right of the junction represent the available electrons from the ntype dopant.
The band diagrams of 1 and 2 by themselves are shown below. Sketch the carrier concentration of both electrons and holes as a function of position. The pn junction is a versatile element, which can be used as a rectifier, as an isolation structure and as a voltagedependent. When looking at a band diagram, the electron energy states bands in a material can curve up or down near a junction. In tunnel diode, electric current is caused by tunneling. Pn junction diode and characteristics of pn junction diode. E v to be positive if e v,n energy diagram for zener diode.
Energy band diagram of a pn junction a before and b after merging the ntype and ptype regions note that this does not automatically align the fermi energies, e f,n and e f,p. There are a few basic concepts to be introduced, such as energy bands, drift and. In this lecture, i discussed about the energy band diagram of the pn junction in equilibrium. Pn junction diode baising and its vi characteristics. Pn junction diodes form the basis not only of solar cells, but of many other electronic devices such as leds, lasers, photodiodes and bipolar junction transistors bjts. Near the junction, electrons diffuse across to combine with holes, creating a depletion region. Semiconductor, silicon, pn junction, forward bias, reverse bias, diode. The band structure of a semiconductor gives the energy of the electrons on the yaxis and is called a band diagram. When a bond is supplied with this amount of energy or more an electron can break free of an atom and the electron is then free to move throughout the crystal. In an ideal mos capacitor, the metal work function. A pn junction at equilibrium is characterized by a depletion region where. This is the voltage required to reach a flat band diagram and sets an upper limit typically an overestimate for the voltage that can be applied to a diode before it burns itself up.
Draw the energy band diagram of pn junction diode in forward. Pn junction diode in the reversebiased configuration is sensitive to light from a range between 400nm to nm, which includes visible light. Assume that interface states pin the fermi energy to the middle of the semiconducting gap at the interface. Equilibrium band diagrams appear below the semiconductor. The panels show energy band diagram, electric field, and net charge density. However, the structure of these energy levels is the same for all atoms. For electron energy plotted against wave vector, see band structure. A simple circuit diagram is shown below, which has a pn junction diode, a battery in picture it is not shown as variable. It does not correspond to any physical spatial bending. Therefore, when the fermi level of the semiconductor, e fs, is aligned with the fermi level of the gate, e fm, there is no band bending in any region of the mos capacitor.
Simplified energy band diagram and iv characteristics of the tunnel diode at a forward bias for which the diffusion current dominates. The energy band diagram of the ntype semiconductor and metal is shown in the below figure. The energy level sketch above right is a way to visualize the equilibrium condition of the pn junction. Band diagram of pn junction under a equilibrium and b forward bias. The second theory of reverse breakdown effect in diodes is known as avalanche breakdown and occurs at reverse voltages beyond 5 volts. Pn and metalsemiconductor junctions the gmu ece department. This pn diode applications are very useful for beginners. Jan 29, 2019 pn junction diode is one of the fundamental elements in electronics. Draw the energy band diagram of pn junction diode in forward and reverse bias condition. Energy band diagram of a pn junction under reverse and forward bias pnjuntion diode. Denote drift, diffusion, and illumination currents. Schottky diode draw the band diagram valence band, conduction band, fermi energy for a schottky diode with a n doped semiconductor and a p doped semiconductor at zero bias.
An energy diagram for a pn junction at the instant of formation is shown in figure a. Apr 05, 2019 working of pn junction diode if an external potential is applied to the terminals of pn junction, it will alter the potential between the p and nregions. Consider the the band diagram for a homojunction, formed when two bits of the same type of semiconductor e. The energy band diagram of a np heterojunction diode in thermal equilibrium. The energy band diagram would provide us with i a qualitative variation of potential in the device ii boundary conditions for solution of poissons equation as usual, the energy band diagram of the pn junction will be obtained by combining the energy band diagrams of n and ptype semiconductors separately energy band. Energy band diagram of a pn junction a before and b after. This article is about electron energy plotted against position. The lower energy level of a semiconductor is called the valence band e v and the energy level at which an electron can be considered free is called the conduction band e c. What is the currentvoltage characteristic for the pn junction diode. A pn junction consists of two semiconductor regions with opposite doping type as. The energy band diagram of an ideal ptype substrate mos capacitor at zero bias is shown in figure 3. Pn junction diode and diode characteristics electronicstutorials. However if the diode terminals are shorted together, a few holes majority carriers in the ptype material with enough energy to overcome the potential barrier will. Energy band diagram at thermal equilibrium at thermal equilibrium energy band diagram of a pn junction in thermal equilibrium while in thermal equilibrium no external voltage is applied between the ntype and ptype material, there is an internal potential, f, which is caused by the workfunction difference between the ntype and ptype pn.
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. 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 an nside bringing an extra negative charge in there pn. Semiconductor physics semiconductors and diodessemiconductors. Also, note that this flatband diagram is not an equilibrium diagram since both electrons and holes can lower their energy by crossing the junction. This potential difference can alter the flow of majority carriers, so that the pn junction can be used as an opportunity for the diffusion of electrons and holes. Pn junction diode is one of the fundamental elements in electronics. In this video, i go over the band diagram of the pn junction, which will allow us to find the electric field and the pn junction width through what is called the builtin potential vbi. In this type of diode, we dope one side of a semiconductor piece with an acceptor impurity and another side with a donor impurity. When a diode is connected in a zero bias condition, no external potential energy is applied to the pn junction. 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.
Tunnel diode is a highly doped semiconductor device and is used mainly for low voltage high frequency switching applications. In a p on n structure, this can be accomplished by inserting an electronblocking unipolar barrier at the junction of the pn diode to form the pbn diode klipstein, 2008. A pnjunction 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 pn junction the pn junction is a homojunction between a ptype and an ntype semiconductor. If a suitable positive voltage forward bias is applied between the two ends of the pn junction, it can supply free electrons and holes with the extra energy they.
The tunnel diode is used as a very fast switching device in computers. A pn junction diode is a twoterminal electronics element, which can be classified as either. Forward bias current flows reverse bias no current flow. Here dec is the change in the energy of the conduction band across the junction. Draw the energy level diagram of a pn junction and explain how a junction barrier is developed across an unbiased junction. Tunnel diode working principle and characteristics ece. There are a few basic concepts to be introduced, such as energy bands, drift and diffusion currents, etc. The energy band diagram of a pn junction showing the location of carriers under zero voltage bias 1. Working of pn junction diode if an external potential is applied to the terminals of pn junction, it will alter the potential between the p and nregions. 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. A pn junction aggregates the recombination, generation, diffusion and drift effects described in the previous pages into a single device. A pn junction diode is a twoterminal electronics element, which can be classified as either step graded or linear graded. E v to be positive if e v,n energy band diagram of a pn junction a before and b after merging the ntype and ptype regions note that this does not automatically align the fermi energies, e f,n and e f,p. As shown in the figure, pn junction diode is a 2 terminal polarity sensitive device.
Reducing depletion width can be inferred from the shrinking charge profile, as fewer dopants are exposed with increasing forward bias. Note to those familiar with a diode turn on voltage. Band edge diagram zwhen we draw a band edge diagram out of equilibrium, we need to draw a different fermi level quasifermi level for the electrons and holes zthis, for example, is what the band edge diagram would look like for a forward biased pn diode quasi fermi level for electrons quasi fermi level for holes exactly. Schottky diode definition, symbol, working and applications. It is also used in highfrequency oscillators and amplifiers. This potential difference can alter the flow of majority carriers, so that the pn junction can be used as an opportunity for the diffusion of. Shur introduction to electronic devices energy band diagram of a pn junction silicon pn junction at zero bias.
No electrons on the n side are directly opposite to the empty states on the p side. A schottky diode is the preferred rectifier in low voltage, high current applications. The pn junction is the fundamental building block of the electronic age. Pn junction diode applications pn diode applications. I0 of a schottky diode is 103 to 108 times larger than a pn junction diode, depending on. The electric field results from the deviation from charge neutrality in the vicinity of the junction. A diode is a simple device, which can be implemented by a pnjunction, as well as other heterojunction structures. E equilibrium currents for pn junction in equilibrium there. Energy diagram for pn junction the potential energy difference between the two sides of the junction is given by electric field in the depletion region. Also, note that this flatband diagram is not an equilibrium diagram since both electrons and holes can. This page of application notes section covers pn junction diode applications. A tunnel diode is a heavily doped pn junction diode in which the electric current decreases as the voltage increases.
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