Questions you should be able to answer by the end of todays lecture. Tunnel diode working principle and characteristics ece. Semiconductor physics semiconductors and diodessemiconductors. A light emitting diode led is an optical semiconductor device that emits light when voltage is applied. A diode is a simple device, which can be implemented by a pn junction, as well as other hetero junction structures. Chapter 1 semiconductor pn junction theory and applications. For lightly doped diode, which has doping concentration less than 10 15 cm3. Apr 05, 2019 in this tutorial, we will learn about pn junction diodes and in particular the characteristics and working of pn junction diode. It acts as a diode, which can serve in electronics as a rectifier, logic gate, voltage regulator zener diode. Silicon a single silicon atom consists of fourteen negatively.
The two semiconductors are not necessarily the same, e. The pn junction is used an electronic circuit element called the diode. It does not correspond to any physical spatial bending. The upward direction in the diagram represents increasing electron energy.
Energy band diagram of a pn junction under reverse and forward bias pnjuntion diode. Denote drift, diffusion, and illumination currents. When ptype and ntype materials are placed in contact with each other, the junction behaves very differently than either type of material alone. In this tutorial, we will learn about pn junction diodes and in particular the characteristics and working of pn junction diode. Note to those familiar with a diode turn on voltage. Pn junction is a significant building block and it is one among the indispensable structures. In other words, led is an optical semiconductor device that converts electrical energy into light energy. They are also called pn diodes in analogy with vacuum diodes. Jan 29, 2019 pn junction diode is one of the fundamental elements in electronics. 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. Pn junction diode and characteristics of pn junction diode. Diode water model if a voltage source is oriented in a circuit so that the intended current.
Energy band diagram of a pn junction a before and b after merging the ntype and ptype regions. The forwardbias and the reversebias properties of the pn junction imply that it can be used as a diode. E equilibrium currents for pn junction in equilibrium there are still small currents flowing across. Pn junction diode is integral for all electronic devices to operate, aggregating all forms of carrier transport, generation, and recombination. Consider the the band diagram for a homojunction, formed when two bits of the same type of semiconductor e. The energy band diagram of an ideal ptype substrate mos capacitor at zero bias is shown in figure 3. A pn junction diode is a twoterminal electronics element, which can be classified as either step graded or linear graded. 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. E equilibrium currents for pn junction in equilibrium there. Pn junction diode is one of the fundamental elements in electronics. Energy band diagram an overview sciencedirect topics. Electrons and holes remain staying close to the pn junction because. Also, note that this flatband diagram is not an equilibrium diagram since both electrons and holes can. When looking at a band diagram, the electron energy states bands in a material can curve up or down near a junction.
To return the semiconductor to separate pieces, click the separate button or drag one object away from the other. Majority carriers can diffuse across the pn junction depletion region, even though the electric field impedes their crossing. Assume that interface states pin the fermi energy to the middle of the semiconducting gap at the interface. Define parameters that determine solar cell efficiency. Forward bias current flows reverse bias no current flow. Schottky diode definition, symbol, working and applications. How depletion region is developed in a schottky diode. 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. A diode is a simple device, which can be implemented by a pnjunction, as well as other heterojunction structures. In a normal pn junction diode, a ptype semiconductor and an ntype semiconductor are used to form the pn junction.
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. What happens when we join ptype and ntype semiconductors. A simple circuit diagram is shown below, which has a pn junction diode, a battery in picture it is not shown as variable. An excellent detailed treatment can be found in wolfe et al. Common diode packages and markings diodes often have their cathode end marked with a band. Most semiconductor devices involve regions with two different kinds of doping, so a pn junction is present in all of them.
Pn junction diode in the reversebiased configuration is sensitive to light from a range between 400nm to nm, which includes visible light. The band diagram of a pn and metal semiconductor junctions. A light emitting diode led is essentially a pn junction diode. I0 of a schottky diode is 103 to 108 times larger than a pn junction diode, depending on. 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. Specifically, current will flow readily in one direction forward biased but not in the other reverse biased, creating the basic diode. 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. A pn junction diode allows electric charges to flow in one direction, but not in the opposite direction. The pn junction is a versatile element, which can be used as a rectifier, as an isolation structure and as a voltagedependent. Hi what could be the band diagram of pnjunction diode at very low temperature where dopant ionzation is completely frozen out. Pn junction diode baising and its vi characteristics. Light emitting diode led working, construction and. Similarly due to the increase in the hole density in the valence band of the p side, the fermi level moves downwards.
The symbol of led is similar to the normal pn junction diode except that it contains arrows pointing away from the diode indicating that light is being emitted by the diode. Conversely, the energy for the positively charged hole increases when going downward in this band diagram. Most semiconductor devices involve regions with two different kinds of doping, so a pnjunction is present in all of them. Schottky diode is a metalsemiconductor junction diode that has less forward voltage drop than the pn junction diode and can be used in highspeed switching applications. Semiconductor, silicon, pn junction, forward bias, reverse bias, diode. In an ideal mos capacitor, the metal work function. 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. 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. The energy band diagram of a pn junction showing the location of carriers under zero voltage bias 1. An energy diagram for a pn junction at the instant of formation is shown in figure a.
In this type of diode, we dope one side of a semiconductor piece with an acceptor impurity and another side with a donor impurity. Formation of a pn junction diode and its band diagram. A pn junction diode is a twoterminal electronics element, which can be classified as either. This understanding will lay a better foundation for exploring further into different aspects of semiconductor electronics. Also, the schottky diode produces less unwanted noise than pn junction diode. 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 most common colors of leds are orange, yellow, green and red. When light emitting diode led is forward biased, free electrons in the conduction band recombines with the holes in the. Most of the commercial leds are realized using a highly doped n and a p junction. The energy band diagram of a quantum well is shown in fig. Also, note that this flatband diagram is not an equilibrium diagram since both electrons and holes can lower their energy by crossing the junction. 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. 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. The band structure of a semiconductor gives the energy of the electrons on the yaxis and is called a band diagram.
A schottky diode is the preferred rectifier in low voltage, high current applications. Draw the energy band diagram of pn junction diode in forward and reverse bias condition. Would it still be like the band diagram at room temperature. Semiconductor diodes the diode is the simplest type of semiconductor device. The tunneling phenomenon only takes place in heavily doped diodes such as zener diodes. 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.
Is it possible for the fermi energy level of a metal to be lower than the valence band maximum of a. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction. The energy band diagram of a pn junction showing the location of carriers under forward bias voltage. When carriers are injected across a forwardbiased junction, it emits incoherent light. 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. Therefore a hole in the ptype region of the pn junction encounters an electrical potential barrier when trying to move into the ntype region.
The energy level sketch above right is a way to visualize the equilibrium condition of the pn junction. For a pn junction at equilibrium, the fermi levels match on the two sides of the junctions. Prior to voltage being applied to the diode, at the junction of the ptype and ntype regions, free. A pn junction aggregates the recombination, generation, diffusion and drift effects described in the previous pages into a single device. Draw the energy band diagram of pn junction diode in. Schottky diode can switch on and off much faster than the pn junction diode. Band diagram of pn junction under a equilibrium and b forward bias. A pn junction at equilibrium is characterized by a depletion region where. Lets get a voltmeter and ammeter and connect it to the forward biased circuit of pn junction diode. Energyband diagram showing a pn junction a under forward bias positive voltage applied to ptype material and b under reverse bias, c minoritycarrier.
Oct 05, 2017 in this lecture, i discussed about the energy band diagram of the pn junction in equilibrium. The pn junction biasing the pn junction the diode trouble shooting. In order to initiate the junction formation, click the formjunction button or mouse drag one object toward the other. These two characteristics of the schottky diode make it very useful in highspeed switching power circuits. The schematic symbol of led does not represent the color of. Electrons and holes reach an equilibrium at the junction and form a depletion region. This makes the charge flow through the junction easier. The pn junction is the fundamental building block of the electronic age. Here dec is the change in the energy of the conduction band across the junction. What is the currentvoltage characteristic for the pn junction diode. Band diagram of pnjunction diode at low temperature. For a pin junction the above expressions take the following modified form. Electrons in the two bits have different electrochemical potentials i.
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. Image source forward biasing a pn junction diode is very simple. When the diode is passing current we say it is forward biased. There are a few basic concepts to be introduced, such as energy bands, drift and diffusion currents, etc.
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. This yields the socalled flatband diagram shown in figure. Near the junction, electrons diffuse across to combine with holes, creating a depletion region. In this lecture, i discussed about the energy band diagram of the pn junction in equilibrium. 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. Forward biasing increases the electron density in the conduction band of the nside. 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. The band gap of a semiconductor is the minimum energy required to excite an electron that is stuck in its bound state into a free state where it can participate in conduction. The band diagrams of 1 and 2 by themselves are shown below. Pn junction one of the crucial keys to solid state electronics is the nature of the pn junction. 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. Energy band diagram of a pn junction a before and b after.
Draw the energy band diagram of pn junction diode in forward. Pn and metalsemiconductor junctions higher education. Working of pn junction diode with biasing, characteristics. Basic diode electronics introduction to diodes the pn junction the pn junction is a homojunction between a ptype and an ntype semiconductor. 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. 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. 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.
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