PN junction diode is a diode which can be used as a rectifier, logic gate, voltage stabiliser, switching device, voltage dependent capacitor and in optoelectronics as a photodiode, light-emitting diode (LED), laser diode, photo detector, or solar cell in electronics. P-N junction diode is a two-terminal polarity sensitive device, the diode conducts when in forwarding bias and diode not conducts when reverse bias. The word diode is a contraction of two electrodes, where di stands for two. As the concentration of holes is high in the p-type region and it is low in the n-type region, the holes start diffusing from the p-type region to the n-type region. when it is reverse biased) while the reverse voltage is within a specified range. In the same way, the holes diffusing into the n-type region from the p-type region would recombine with free electrons available there and create uncovered positive ions in the n-type region. In this way, there would a layer of negative ions in the p-type side and a layer of positive ions in the n-type region appear along the junction line of these two types of semiconductors. Due to the lack of charge carriers, this region is called the depletion region. The name diode is derived from “di-ode,” meaning a device that has two electrodes. P-N Junction Diode Junction Diode Symbol and Static I-V Characteristics: Fig.2. Name. The number of electrons is balanced by the number of protons in both blocks. Fig-1b: Diode Symbol. In the beginning, there is no current flowing through the diode. Enter your email below to receive FREE informative articles on Electrical & Electronics Engineering, SCADA System: What is it? Default. Precaution. Today, we’ll talk about P-N junction diode. This current is called reverse saturation current. The pn Junction Diode Schematic diagram p-type n-type ID + V D – Circuit symbol Physical structure : (an example) p-type Si n-type Si SiO 2 SiO 2 metal metal + ID VD – net donor concentration ND net acceptor concentration NA For simplicity, assume that the doping profile changes abruptly at the junction. The literal meaning is that the cathode is connected to the n side, and the anode is connected to the p side. The potential of the layer of uncovered positive ions in the n-type side would repeal the holes in the p-type side and the potential of the layer of uncovered negative ions in the p-type side would repeal the free electrons in the n-type side. There are three possible biasing conditions for the PN Junction: Equilibrium or Zero Bias – No external voltage is applied to the PN junction. In ideal conditions, this PN junction behaves as a short circuit when it is forward biased, and as an open circuit when it is in the reverse biased. Now let us see what happens if a positive terminal of a source is connected to the p-type side and the negative terminal of the source is connected to the n-type side of the diode and if we increase the voltage of this source slowly from zero. This gives it its name: "di-" meaning two and "-ode" as a shortening of electrode. The problem is two separate and distinct crystal bodies. A diode is effectively like a valve for an electrical circuit. The arrowhead points in the direction of conventional current flow in the forward biased condition. A diode is a two-terminal unidirectional power electronics device. Figure (c) PN junction diode in reverse bias . Thus, neither block has any net charge. On n-side there are large number of electrons on other hand p-side is having more number of holes. Again the concentration of free electrons is high in the n-type region and it is low in the p-type region and due to this reason, free electrons start diffusing from the n-type region to the p-type region. Symbol Representing P-N Junction Diode The symbol has been designed in such a way that it has an arrowhead pointing in the direction showcasing the flow of direction of the current. When the voltage of the circuit is higher than the reverse breakdown voltage, the diode is able to conduct electricity in the reverse direction (i.e. The schematic symbol of a PN junction diode is shown in figure 1-12. ⦁ It conducts current only in one direction⦁ It consists two terminals are called electrodes, one from p-region and one from n-region⦁ The p region is anode while the n region is cathode⦁ Biasing is applying the external voltage to the p-n junction diode⦁ Biasing is having two types :   I. As a result, there is a tiny current flowing through the diode from positive to the negative side. This condition of a diode is called the reverse biased condition. The arrow head in the schematic symbol of a p-n junction indicates the direction of conventional current flow when the diode is forward biased. Description. A PN junction is the simplest form of the semiconductor diode. This is due to the electric field appeared across the depletion region will prevent further migration of charge carriers from one side to another. The name diode is derived from “di–ode” which means a device that has two electrodes. An ideal diode (pn- or schottky-diode) generates shot noise. What is the mystery about the death of Indian scientists? A diode only blocks current in the reverse direction (i.e. the “high resistance” direction). Full disclaimer here. Electrical4U is dedicated to the teaching and sharing of all things related to electrical and electronics engineering. Model parameters must be specified in SI units. In ideal conditions, this PN junction behaves as a short circuit when it is forward biased, and as … Both types of current (field and diffusion) contribute independently to it. If a block of P-type semiconductor is placed in contact with a block of N-type semiconductor in Figure below(a), the result is of no value. These opposite charge carriers in a semiconductor are called minority charge carriers. These dopings make a PN junction in the middle part of the block. The diode symbol is given below. But today also the most commonly used diode is a semiconductor diode. The label "CR1" is an alphanumerical code used to identify the diode. We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites. The symbol of a diode is shown below. A PN junction is the simplest form of the semiconductor diode. That means the anode is connected to the p-type and cathode is connected to the n-type. Like any diode, the PN junction diode has two connections or electrodes. The diode symbol is … Diodes are commonly used in many electronics projects and are included in many of the best Arduino starter kits. 2. One electrode of the semiconductor device is termed the anode and the other is termed the cathode. I am going to cover all the diodes in my some of the next blogs. And the working of this PN junction diode under forward and reverse bias has been explained. The vertical bar represents the cathode (N-type material) since it is the source of electrons and the arrow represents the anode. These diodes begin conducting electricity only if a certain threshold voltage is present in the forward direction (i.e. Here due to concentration differences, majority carriers diffuse from one side to another. The diode is a semiconductor device that allows the current to flow in one … For silicon diodes, the forward barrier potential is 0.7 volt and for germanium diodes, it is 0.3 volt. Observe the different quasi Fermi levels for conduction band and valence band in n and p regions (red curves). Diode Symbol. The amplitude of this current is very small as the number of minority charge carriers in the diode is very small. The majority charge carriers start crossing the forward potential barrier only when the value of externally applied voltage across the junction is more than the potential of the forward barrier. Below, the symbol of the diode is shown. How P-N junction is formed. Physics(Science) is just name of steady pain-in-the-ass effort. Symbol of tunnel diode. Diode_Model (PN-Junction Diode Model) Symbol Parameters. A PN crystal is commonly known as junction diode. At that condition, no majority carriers cross the junction, and they instead move away from the junction. The layers of uncovered positive ions and uncovered negative ions form a region in the middle of the diode where no charge carrier exists since all the charge carriers get recombined here in this region. cross-sectional area AD What is a pn junction? A PN junction with two metallic contacts is known as a pn junction diode or a semiconductor diode. interface or a boundary between two semiconductor material types The negative signal explains a negative recombination rate; therefore, we’re actually generating electron-hole pairs inside the reverse-biased space charge region. Bi-directional Photo Diode A generic photo diode is designed to operate in only reverse bias. Without knowing the basic idea of p-type and n-type materials, pn junction, depletion region and barrier potential, we are unable to understand the working of a diode as well as a transistor and many other electronic devices. Fig-1: PN Junction diode. 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