A pn junction diode is referred to as a minority carrier device since its. 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, ef,n and ef,p. Abrupt pn junction diode, point contact diode, opto coupler, schottkey diode in hindi 10. This band alignment is due to the biasing conditions that correspond with forwardactive mode. Semiconductor pn junction diode is the simplest semiconductor device. Minority carrier depletion region tunnel diode dopant density energy band diagram.
The height of the conduction hill reduces by the same amount. With the diode check function a good diode will show approximately. A pn junction diode is twoterminal or twoelectrode semiconductor device, which allows the electric current in only one direction while blocks the electric current in opposite or reverse direction. Large and small signal modelling of pn junction diodes in this lecture you will learn. Draw the energy band diagram of pn junction diode in forward and reverse bias condition. In this type of diode, we dope one side of a semiconductor piece with an acceptor impurity and another side with a donor impurity. Energy band diagram of p n junction diode in open circuited condition and derivation for contact potential in hindi hindi basics of semiconductor diode. The energy band diagram of the metal and ntype semiconductor after contact is shown in figure b. Speaking of band diagrams in describing semiconductor devices i cant. The energy band diagram of the pn junction under open circuit conditions is shown in figure 6. 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. Since the p n junction demonstrates such a unipolar rectifying response to the applied voltage it is called a p n diode and is denoted in circuit diagrams as a following symbol. Energyband diagram of a pn junction under reverse bias under reverse bias of applied voltage v r, the pn junction is not in thermal equilibrium.
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. See the figure in in band diagram, why the fermi energy ef is constant along the device. Electrons and holes reach an equilibrium at the junction and form a depletion region. 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. 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. The depletion region extends mainly into the pside. Find the minority carrier concentrations in the neutral regions of the n and psides. The band gap is the minimum amount of energy required for an electron to break free of its bound state. To plot characteristics between reverse saturation current and 10 3t and find out the approximate value of energy band gap in pn junction diode apparatus. 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.
The fermi levels and are displaced relatively by an amount ev equal to the potential energy due to the applied voltage, v which cause the displacement. Draw the energy band diagram of an unbiased pn junction and mark the barrier potential and depletion region. Simplified energyband diagram and iv characteristics of the tunnel diode at a forward bias for which the diffusion current dominates. When looking at a band diagram, the electron energy states bands in a material can curve up or down near a junction. For a p n junction at equilibrium, the fermi levels match on the two sides of the junctions. Pn junction one of the crucial keys to solid state electronics is the nature of the pn junction. The second theory of reverse breakdown effect in diodes is known as avalanche breakdown and occurs at reverse voltages beyond 5 volts. When ptype and ntype materials are placed in contact with each other, the junction behaves very differently than either type of material alone. 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. 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. Testing a diode is quite simple, particularly if the multimeter used has a diode check function. Pn junction diode baising and its vi characteristics. Shur introduction to electronic devices energy band diagram of a pnjunction silicon pnjunction at zero bias. Develop an understanding of the pn junction diode and its behavior.
Energy band diagram for equilibrium of junction potential barrier the electric field formed in the depletion region acts as a barrier. Lecture 7 large and small signal modelling of pn junction. Define parameters that determine solar cell efficiency. A tunnel diode is a heavily doped pn junction diode in which the electric current decreases as the voltage increases. The normal ideal diffusion current exists in the device. They readily combine with those holes, making possible a continuous forward current through the junction. Reducing depletion width can be inferred from the shrinking charge profile, as fewer dopants are exposed with increasing forward bias. With the diode check function a specific known voltage is applied from the meter across the diode. 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. An energy diagram for a pn junction at the instant of formation is shown in figure a. Equilibrium band diagrams appear below the semiconductor.
The default pnjunction device geometry we use in our analyses, including two alternative coordinate systems for convenience. A pn junction of two different materials in the open circuit case. 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. Oct 05, 2017 in this lecture, i discussed about the energy band diagram of the pn junction in equilibrium. Note to those familiar with a diode turn on voltage. It is also required to obtain the capacitancevoltage characteristics of the diode. The panels show energy band diagram, electric field, and net charge density. In tunnel diode, electric current is caused by tunneling. The area of the ptype near the junction becomes more negative due to the excess electrons while the ntype. If the diode is forward biased, it allows the electric current flow. In silicon, the bonding energy of the covalent bond is 1.
If somebody is able to understand pn junctions well, it becomes quite easy for him to understand all other. I attach a pdf file of one of my lectures where i explain this stepbystep. The quasifermi energy levels for electrons and holes are ln 0 n fn fi i n e e kt n g. Circuit models of pn junction diodes small signal modeling of nonlinear circuit elements small signal models of pn junction diodes junction resistance and capacitances. A steadystate balance of carriers is achieved at the junction where diffusive flux of the carriers is balanced by the drift flux. The electric field results from the deviation from charge neutrality in the vicinity of the junction. Introduction to diodes advanced energy technology program. Which can be understood from the energy band diagram shown above. Eeng 421 semiconductor device physics and design fall 2016. For a pn junction at equilibrium, the fermi levels match on the two sides of the junctions. The upward direction in the diagram represents increasing electron energy. Use a band diagram to explain how a pn junction diode works 3. Semiconductors, diodes, transistors horst wahl, quarknet presentation, june 2001 electrical conductivity.
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. A diode is a simple device, which can be implemented by a pnjunction, as well as other heterojunction structures. Simplified energy band diagram and iv characteristics of the tunnel diode at a forward bias for which the diffusion current dominates. Jan 29, 2019 pn junction diode is one of the fundamental elements in electronics. Band gap is the energy difference between the top of valance band and the bottom of conduction band for small inter distance. Therefore, a drift current and a diffusion current is flowing. Specifically, current will flow readily in one direction forward biased but not in the other reverse biased, creating the basic diode. There is an energy gradient across the depletion region that a n region electron must climb to get to the p region. A pn junction consists of two semiconductor regions with opposite doping type as.
It is noteworthy that the drift currents remain the same for di erent biasing conditions. There is no net current, so the diffusion current of electrons from the n to pside is balanced by the electron drift current from the p to nside driven by the builtin field e0. Physics stack exchange is a question and answer site for active researchers, academics and students of physics. 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. Ece 255, pn junction and diode college of engineering. In solidstate physics of semiconductors, a band diagram is a diagram plotting various key electron energy levels fermi level and nearby energy band edges as a function of some spatial dimension, which is often denoted x. No electrons on the n side are directly opposite to the empty states on the p side.
Because of its electrical properties, silicon is called a semiconductor. Realise the pn junction behaviour when applying a dcvoltage. Energy band gap apparatus containing micrometer, voltmeter, temperature controlled electric oven to heat up the diode, pn junction. External energy must be applied to get the electrons to move across the barrier of the electric field. Also, note that this flatband diagram is not an equilibrium diagram since both electrons and holes can. 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. It does not correspond to any physical spatial bending. Depletion region created across the pn junction by the initial movement of majority carrier across the junction. The band gap determines how much energy is needed from the sun for conduction, as well as how much energy is generated. 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. In this lecture, i discussed about the energy band diagram of the pn junction in equilibrium.
Working of pn junction diode with biasing, characteristics. There are a few basic concepts to be introduced, such as energy bands, drift and diffusion currents, etc. Most semiconductor devices involve regions with two different kinds of doping, so a pnjunction is present in all of them. A pn junction diode is a twoterminal electronics element, which can be classified as either. A pn junction diode is a twoterminal electronics element, which can be classified as either step graded or linear graded.
We can then fill in the junction region of the band diagram as. That implies that you would have to supply energy to get an electron to go up on the diagram, and supply energy to get a hole to go down. Semiconductor pn junction diode working pn diode vi. Tunnel diode definition, symbol, and working diode. Find the doping concentrations in the n and psides, respectively. One terminal of pn junction diode is anode and other is cathode. It acts as a diode, which can serve in electronics as a rectifier, logic gate, voltage regulator zener diode, switching or tuner varactor diode. It is also used in highfrequency oscillators and amplifiers. 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. Indicate conduction and valence bands, intrinsic fermi level and fermi level in your sketch. Dec 27, 2017 this video provides knowledge on how to draw the energy band diagran for a pn junction.
Energy band diagram at thermal equilibrium at thermal equilibrium energy band diagram of a p n 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. Also, note that this flatband diagram is not an equilibrium diagram since both electrons and holes can lower their energy by crossing the junction. So the answer is that using the simply common model of the diode. Qualitatively explain the formation of the depletion region and the.
Think about it if you were right, all the diodes of a given material would have the same builtin potential. Formation of a pn junction diode and its band diagram. Semiconductor physics semiconductors and diodessemiconductors. Doped semiconductors ntype materials ptype materials diodes and transistors. Video created by georgia institute of technology for the course introduction to electronics. 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. These diagrams help to explain the operation of many kinds of semiconductor devices and to visualize how bands change with position band bending.
Barrier potential in a pn junction refers to the potential required to overcome the barrier at the pn junction. Pn junction diode in the reversebiased configuration is sensitive to light from a range between 400nm to nm, which includes visible light. Spring 2003 ee lecture 10, slide 4 idealized junctions. The tunnel diode is used as a very fast switching device in computers. Denote drift, diffusion, and illumination currents. Relationship between band gap and built in potential for pn. The pn junction the pn junction is a homojunction between a ptype and an ntype semiconductor. 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.
A pn junction is a boundary or interface between two types of semiconductor materials, ptype. Valence band p n forming a pn junction electrons continue to diffuse across the junction. A pn junction under di erent bias conditions, showing transition region width, electric eld, electrostatic potential, and energy band diagram, for a equilibrium, b forward biased, and c reverse biased courtesy of streetman. Draw the energy band diagram of pn junction diode in. Energy band diagram of a pn junction a before and b after. When the band gap energy is met, the electron is excited into a free state, and can therefore participate in conduction. When the pn junction is forward biased, the electrons in the ntype material which have been elevated to the conduction band and which have diffused across the junction find themselves at a higher energy than the holes in the ptype material. Describe how innovations in semiconductor devices the integrated circuit, high efficiency white leds, improved solar cells has changed our world modern computing, energy efficiently lighting, alternative energy. Depletion layer opposes only the the majority carrier not minority carrier.
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