Realise the pn junction behaviour when applying a dcvoltage. Any applied voltage must therefore drop across the scl. A diode is a simple device, which can be implemented by a pn junction, as well as other hetero junction structures. Most semiconductor devices involve regions with two different kinds of doping, so a pn junction is present in all of them. Semiconductors diodes transistors phet interactive. The energy band diagram of the metal and ntype semiconductor after contact is shown in the below figure. Pn junction diode in the reversebiased configuration is sensitive to light from a range between 400nm to nm, which includes visible light. Unit i semiconductor diode ec8252 electronic devices notes. When a pn junction is forward biased then its energy band diagram looks like this. The forwardbias and the reversebias properties of the pn junction imply that it can be used as a diode. In order to initiate the junction formation, click the formjunction button or mouse drag one object toward the other. However, the structure of these energy levels is the same for all atoms.
With the diode check function a specific known voltage is applied from the meter across the diode. A pn junction diode is a twoterminal electronics element, which can be classified as either step graded or linear graded. This video provides knowledge on how to draw the energy band diagran for a pn junction. The band gap is small enough that at room temperature some electrons move to the conduction band and material conduct electricity. Semiconductors pn junction theory interview questions and answers pdf free download. The band gap is the minimum amount of energy required for an electron to break free of its bound state. The figure shows a band bending diagram for a pn diode. Silicon a single silicon atom consists of fourteen negatively. As shown in the figure, pn junction diode is a 2 terminal polarity sensitive device. When the metal is joined with the ntype semiconductor, a device is created known as schottky diode. A pn junction diode is a twoterminal electronics element, which can be classified as either.
Formation of a pn junction diode and its band diagram. Draw to scale the energy band diagram of the junction at equilibrium. For example, a common type of transistor, the bipolar junction transistor, consists of two pn junctions in series, in the form n pn or pn p. Step pn junction energy band diagram physics forums. The word diode can be explained as di means two and ode is obtained from electrode. Doped semiconductors ntype materials ptype materials diodes and transistors. Pn junction diode, current equations, energy band diagram, diffusion and drift current densities, forward and reverse bias characteristics, transition and diffusion capacitances, switching characteristics, breakdown in pn junction. Testing a diode is quite simple, particularly if the multimeter used has a diode check function. The depletion region is free of mobile charge carriers.
Pn junction diode is a two terminal device, the characteristics of diode depends on the polarity of the external potential applied to the pn junction diode. 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. A schottky junction is a special case of a pn junction, where metal serves the role of the ptype semiconductor. Luminescence study in ingaasalgaas multiquantumwell. Apr 05, 2019 pn junction diode is a two terminal device, the characteristics of diode depends on the polarity of the external potential applied to the pn junction diode.
So a finite probability that some electrons tunnel directly into the. It is also important to note here that the equilibrium barrier potential can be altered. If positive potential is applied to the top terminal as shown in fig. How does a diode work the pn junction with animation. Pn junction physics and radioelectronics free online. Semiconductor physics semiconductors and diodessemiconductors. Tunnel diode definition, symbol, and working diode. Pn junction diode is one of the fundamental elements in electronics. Sketch the carrier concentration of both electrons and holes as a function of position. Theory of pn junction diode, diode current equation duration. Image source forward biasing a pn junction diode is very simple. Smith department of eecs university of california, berkeley eecs 105 spring 2004, lecture 19 prof. The second theory of reverse breakdown effect in diodes is known as avalanche breakdown and occurs at reverse voltages beyond 5 volts. The free electrons in the n region that occupy the upper part of the conduction band in terms of their energy can easily diffuse across the junction they do not have to gain additional energy and temporarily become free electrons in the lower part of the pregion conduction band.
In this work, we apply pn junction engineering to study electrophotoluminescence spectra under opencircuit, forward voltage, and reverse voltage conditions. Also, note that this flatband diagram is not an equilibrium diagram since both electrons and holes can lower their energy by crossing the junction. Pn junction diode applications pn diode applications. If somebody is able to understand pn junctions well, it becomes quite easy for him to understand all other. Electrons and holes reach an equilibrium at the junction and form a depletion region. The pn junction diode may get destroyed due to excessive heat if any of these values are exceeded.
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. This pn diode applications are very useful for beginners. We can then fill in the junction region of the band diagram as. This type of breakdown diode has a depletion region that is deliberately made narrower than the depletion region in the normal pn junction diode, but thicker than. P type and n type semiconductors, takenseparately are of very limited use. These diagrams help to explain the operation of many kinds of semiconductor devices and to visualize how bands change with position band bending. When the diode is forwardbiased, it can be used in led lighting applications. It does not correspond to any physical spatial bending. Explain why an np junction acts as a diode, allowing current to.
When a bond is supplied with this amount of energy or more an elec tron can break free. In effect, then, if one were to connect the two terminals of the pn junction to form a closed circuit, two currents would be present. If this applied voltage is greater than the builtin potential of the depletion layer, the regular forward current starts flowing through the tunnel diode. Note to those familiar with a diode turn on voltage. 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. After crossing the junction, the electrons quickly lose energy. Now, if we join the two types of semiconductors ptype and ntype together then a new device is formed called as pn junction diode. Jan 29, 2019 pn junction diode is one of the fundamental elements in electronics. A diode is a simple device, which can be implemented by a pnjunction, as well as. Energy band diagram and carrier concentrations for a forwardbiased pn junction.
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. The diode has two terminals called a cathode and an anode. The energy band diagram for each cube is displayed directly below it. Pn junction diode baising and its vi characteristics. When light emitting diode led is forward biased, free electrons in the conduction band recombines with the holes in the valence band and releases energy in the form of light. 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. The energy band diagram of the pn junction under open circuit conditions is shown in figure 6. Sample learning goals recognize that the battery is the driving force in a circuit. Quantum well in a pn junction consider a pn junction with a quantum well located between the n and p region as shown in the figure below. Relationship between band gap and built in potential for pn. Pn junction is also a fundamental building block of many other semiconductor electronic devices such as transistors, solar cells, light emitting diodes, and integrated circuits. Lecture 16 the pn junction diode ii free online course.
There are two distinct bias conditions for a pn junction diode. Secondary coil is connected to the diode through resistors rj, across which output. From the above, it follows that zero power dissipation occurs in an ideal diode. Pn junction tutorial introduction to pn junction diodes. In equilibrium, the fermi energy must be uniform over the semiconductor sample. 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. An energy diagram for a pn junction at the instant of formation is shown in figure a. The energy band diagram of an ideal ptype substrate mos capacitor at zero bias is shown in figure 3. Semiconductors and diodessemiconductors and diodes. Comparison of sbd and frd to facilitate understanding of sbd, the diode consisting of pn junction for example, frd or fast recovery diode is. A perfect diode is a device that only allows current to flow through it in one direction, i. Simplified energy band diagram and iv characteristics of the tunnel diode at a slight forward bias. I have developed a second chapter on the series, which explains the characteristics of pn junction diode. This pn junction forms a most popular semiconductor device known as diode.
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. In pn junction diode, both free electrons and holes carry electric current. It will help you to grasp concepts behind pn junction even better. Find the builtin voltage, and compare with the value measured off. Here you may find a good video with animation, which explains the formation of pn junction. 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. Energy band diagram of the pn junction in equilibrium. Pn junction diode, current equations, energy band diagram, diffusion and drift current densities, forward and reverse bias characteristics, transition and diffusion capacitances, switching characteristics, breakdown in pn junction diodes. The energy band diagram of the pn junction duration.
In this lecture, the educator has discussed how to derive a diode current equation in forward bias and reverse bias. Prepared by textbook based on electronics devices by floyd, prentice hall, 7. Semiconductor pn junction diodes physically, diodes are formed by the interface between two regions of oppositely doped semiconductor i. Semiconductor devices have made a major impact on the way we work and live. Octavian florescu 2 the pn junction diode schematic diagram ptype ntype id. 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. Electrons in the conduction band of the n region are directly opposite to the empty states in the valence band of the p region. Overlapping between the quantumwell structure and pn junction plays an important role in the development of highefficiency gaasbased lightemitting diodes leds. Light emitting diode led working, construction and. The connections are illustrated in the adjacent diagram.
Electrical and telecommunications engineering technology department. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction. This textbook introduces the physical concepts required for a comprehensive understanding of pn junction devices, light emitting diodes and solar cells. For a pn junction at equilibrium, the fermi levels match on the two sides of the junctions. A pn junction diode allows electric charges to flow in one direction, but not in the. When a pn diode is made with ptype and ntype materials, then flow of free charge carriers takes place at the junction. Impurities donors andor acceptors can be added to each side, and the resulting change in the energy band diagram can be observed directly below each cube. Band structure of open circuted pn junction youtube.
This presentation is a very informative piece on pn junction diode an important part of electronics education. 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. Describe how n and p dopants change the structure of electron energy levels in a semiconductor. Imagine a pn junction with metallic contacts at both the ends for application of external voltage.
Tunnel diode working principle and characteristics ece. The fermi level lies close to the conduction band in ntype material and it is close to valence band in ptype material. A steadystate balance of carriers is achieved at the. Working of pn junction diode with biasing, characteristics. The emitted photon energy is approximately equal to the band gap energy of the. The process of emitting light in response to the strong electric field or flow of electric current is called electroluminescence. The band gap determines how much energy is needed from the sun for conduction, as well as how much energy is generated. They readily combine with those holes, making possible a continuous forward current through the junction. 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.
Electronic devices ed ee8252 notes pdf free download. Semiconductors, diodes, transistors horst wahl, quarknet presentation, june 2001 electrical conductivity. The tunneling phenomenon only takes place in heavily doped diodes such as zener diodes. Energy band diagram an overview sciencedirect topics. Sep 24, 2005 a step pn junction diode is made in silicon with the n side having nd 2x1016 cm3 and the p side having a net doping of na 5x1015 cm3. This page of application notes section covers pn junction diode applications. The pn junction is the fundamental building block of the electronic age. The pn junction provides satisfactory performance when operated within these limiting values. Outline semiconductor physics the pn junction biasing the pn junction the diode. Ec8252 electronic devices ed regulation 2017 unit i semiconductor diode.
With the diode check function a good diode will show approximately. Frd fast recovery diode this is a diode comprising pn junction. There are a few basic concepts to be introduced, such as energy bands, drift and diffusion currents, etc. Device physics i pn junctions band diagrams yang p. When the breakdown point of the pn junction is reached, large numbers of minority carriers tunnel across the junction to form the current that occurs at breakdown. Pn and metalsemiconductor junctions higher education. V t1 where i do is reverse saturation current and will be very high in tunnel diode compared to pn junction diode due to high doping concentrations. In an ideal mos capacitor, the metal work function. Unlike a laser diode where the pn junction is forward biased, a photodiode requires a reverse bias of the pn junction.
To return the semiconductor to separate pieces, click the separate button or drag one object away from th. 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. When the band gap energy is met, the electron is excited into a free state, and can therefore participate in conduction. 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. The vacuum diode is a rectifier in that electrons cannot flow from anode to. This means that eventually in vicinity of the junction all free carriers will be depleted leaving. When a stable bond is formed, electrons will occupy the lower energy level and leave. Pn junction diode and characteristics of pn junction diode. The junction of n and p semiconductors is free of charge carriers. The metallurgical junction zone has been depleted of carriers compared with the bulk. Since a junction forms between a p type and n type material it is called as pn junction. A pn junction is a boundary or interface between two types of semiconductor materials, ptype. Fermi energy ef is an average energy of all the free carriers in a sample. At this point, the conduction band and valence band no longer overlap and the tunnel diode operates in the same manner as a normal pn junction diode.
Energy bands bend in the free space charge region, since conduction and valence band positions with respect to the fermi energy levels. Today semiconductor pn junction diode devices are experiencing substantial growth. If we join a piece of p type material to a pieceof n type material such that the crystalstructure remains continuous at the boundary, a pn junction is formed 2. The diode current in a tunnel diode is same as that for normal pn junction diode which is given as i diode i do exp v. A pn junction diode allows electric charges to flow in one direction, but not in the opposite direction. Dec 27, 2017 this video provides knowledge on how to draw the energy band diagran for a pn junction. Energy band gap kit containing a pn junction diode placed inside the. The upward direction in the diagram represents increasing electron energy. Review, pn junctions, fermi levels, forward bias prof j.
The student then brings the material together and can create a number of pn junction devices. 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. This is the symbolical representation of a semiconductor diode in the image above, the arrow indicates the direction of current when the diode is under forward bias. The pn junction is used an electronic circuit element. Junction coming to the equilibrium by balancing the fermi level. In this type of diode, we dope one side of a semiconductor piece with an acceptor impurity and another side with a donor impurity. Jul 06, 2016 the free electrons in the n region that occupy the upper part of the conduction band in terms of their energy can easily diffuse across the junction they do not have to gain additional energy and temporarily become free electrons in the lower part of the pregion conduction band. Ec8252 electronic devices ed regulation 2017 semester 2. Explain, with the help of a circuit diagram, the working of a pn junction diode as a halfwave rectifier. As we increase the applied volatge the drop across the nuentral region increases such that the n side depletion region is always higher in. Specialpurpose diodes 129 actually contain two pn junctions that are connected in reverseparallel i. In a semiconductor at 0 k the conduction band is empty and valance band is full. The diode conducts when forward bias is applied and it will introduce zero resistance in the circuit.
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