A qualitative explanation is given for the physical mechanism that take place in pn junctions. Such junctions show a pronounced rectifying behavior. Semiconductor pn junction diodes can be formed from materials other than silicon, such as germanium, selenium, and a host of semiconductor materials used in. A zener diode when forward biased behaves like an ordinary pn junction diode. Reverse saturation current in a silicon pn junction diode nearly doubles for very a. The boltzmann approximation is to say that the resulting current being small compared with the components of this current, we consider that we are still in quasi equilibrium and therefore that the currents equation is still valid by replacing v bi by v. Characteristics of junction diodes technical articles. Semiconductor, silicon, pn junction, forward bias, reverse bias, diode. Pn junction diode analysis with band diagrams youtube.
The conversion of alternating current into direct current is known as rectification. This pn diode applications are very useful for beginners. Smith department of eecs university of california, berkeley eecs 105 spring 2004, lecture 19 prof. It is used for many forms of rectification for current levels both large and small, as well as high and low voltage levels, and it finds many uses in all manner of electronic circuits. However, unlike a resistor, a diode does not behave linearly with respect to the applied voltage as the diode has an exponential currentvoltage iv relationship. Semiconductor physics semiconductors and diodessemiconductors. Biasing a diode means applying voltage to it so that charges inside it can be made to move towards a particular direction. A pnjunction diode is formed when a ptype semiconductor is fused to an ntype semiconductor creating a potential barrier voltage across the diode junction. Zener diode is a pn junction diode specially designed to operate in the reverse biased mode. In reverse biased pn junction diode, the positive terminal of the battery is connected to the ntype semiconductor material and the negative terminal of the battery is connected to the p.
The pn junction biasing the pn junction the diode trouble shooting. Jan 29, 2019 pn junction diode is one of the fundamental elements in electronics. But this is possible only in case of an ideal diode. If both pside and nside of the diode are lightly doped, depletion region at the junction widens. This condition represents the low resistance path through the pn junction allowing very large currents to flow through the diode with only a small increase in bias voltage.
Pn junction diode is a device which conducts when it is forward biased and does not conduct when it is reverse biased. In the case of normal diodes the diode damages at the break down voltage. Pn junction diode applications pn diode applications. Pn junction diode and its characteristics in chapter 1 understanding the pn junction, we have seen how a pn junction is formed from a ptype and ntype semiconductor. Semiconductor pn junction diodes physically, diodes are formed by the interface between two regions of oppositely doped semiconductor i. When a ptype and ntype material are brought in contact, a number of interesting properties arise.
It acts as a diode, which can serve in electronics as a rectifier, logic gate, voltage regulator zener diode. The diode conducts when forward bias is applied and it will introduce zero resistance in the circuit. 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. Pn junction diode plays a vital role in our electronic fields, because of their unique property current flows in only one direction they are used in many electronic or electrical circuits like rectifiers, switches, clippers, clampers, voltage multipliers in this article, we will learn about what is a pn junction diode and how it works and also effect on pn junction diode with different.
May 20, 2016 in this article, we will look at the characteristics of junction diodes and learn how to analyze circuits containing diodes that operate in the forward, reverse, and breakdown biases. Lecture 15 the pn junction diode i iv characteristics november. After having known about various components, let us focus on another important component in the field of electronics, known as a diode. Jan 21, 2019 what is a pn junction when a ptype semiconductor is suitably joined to an ntype semiconductor, the contact surface is called pn junction. This allows electrical current to pass through the junction only in. The process of applying a potential difference across a pn junction diode to get it ready for its operation is called biasing of pn junction diode. In case of a pn junction there are two bias conditions. The slope of the pn junction diode in forwarding bias shows the resistance is very low. In the positive half cycle, during the time interval 0 to t2, diode d will be forward biased and conduct, i. As shown in the figure, pn junction diode is a 2 terminal polarity sensitive device. Applying forward bias to the pn junction diode causes a low impedance path for the junction diode, allows for conducting a large amount of current known as infinite current. Pn junction diode multiple choice questions answers.
The pn junction is of great importance as it is the main control element for the semiconductor devices. From the above, it follows that zero power dissipation occurs in an ideal diode. Connect currents across scl to get total junction current, i d features and limitations of the model engineering the minority carrier injection across a junction deviations at low and high current levels deviations at large reverse bias 6. The major difference between pn junction and the zener diode is that the pn junction diode allows current to pass only in the forward direction, whereas the zener diode allows the current to flow both in the forward and the reversed direction. At the point of the junction, which we call the metallurgical junction, is where n d n a 0. When we connect ptype region of a junction with the positive terminal of a voltage source and ntype region with the negative terminal of the voltage source, then the junction is said to be forward biased. Objective questions on pn junction diode electrical study. The load resistance r l is connected to these terminals through a pn junction diode d. Review, pn junctions, fermi levels, forward bias prof j. Pn junction diode in the reversebiased configuration is sensitive to light from a range between 400nm to nm, which includes visible light.
The vi characteristics of pn junction diode in forwarding bias are nonlinear, that is, not a straight line. Pn junction diode, characteristics and applications 2020. Pn junction diode is a device made of two semiconductor material joined together with the required amount of impurity. A semiconductor diode is a two terminal electronic component with a pn junction. This is the basic construction of the pn junction diode. A pn junction is the simplest form of the semiconductor diode. Physics of semiconductor devices pn junction depletion width. If the external forward voltage applied on the pn junction diode is increased from zero to 0. Under no voltage or unbiased condition, the pn junction diode does not allow the electric current. The pn junction is a versatile element, which can be used as a. The pn junction diode is a twoterminal device, which is formed when one side of the pn junction diode is made with ptype and doped with the ntype material.
Now, if we join the two types of semiconductors ptype and ntype together then a new device is formed called as pn junction diode. In other words, the ideal diode is a short in the forward bias region and an open in the reverse bias region. A pn junction diode allows electric current when it is forward biased and blocks electric current when it is reverse biased. They are also called pn diodes in analogy with vacuum diodes. Introduction to pn junction the engineering projects. A zener diode when reverse biased can either undergo avalanche break down or zener break down. Lecture 6 biased pn junction diodes and current flow. Vi characteristics of pn junction diode in 3biasing modes. An abrupt silicon pn junction n a 10 16 cm3 and n d 4 x 10 16 cm3 is biased with v a 0. The pand ntype regions are referred to as anode and cathode respectively.
It is likely that the diffusion component will exceed the recombination component at this forward bias this can be easily verified. Apr 05, 2019 in this tutorial, we will learn about pn junction diodes and in particular the characteristics and working of pn junction diode. The pn junction has the very useful property that electrons are only able to flow in one direction. The pn junction is the fundamental building block of the electronic age. This understanding will lay a better foundation for exploring further into different aspects of semiconductor electronics. In other words, an actual diode offers a very small resistance not zero when forward biased and is. Most semiconductor devices contains one or more pn junctions. Depending upon voltage they may be either majority or minority current carriers d. The p positive side contains an excess of holes, while the n negative side contains an excess of electrons in the outer shells of the electrically neutral atoms there. Pn junction diode in practice, no diode is an ideal diode, this means neither it acts as a perfect conductor when forward biased nor it acts as an insulator when it is reverse biased. Pn junction is a significant building block and it is one among the indispensable structures. 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. A pn junction diode in thermal equilibrium you have already seen a pn junction diode in thermal equilibrium.
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. The process by which, a pn junction diode blocks the electric current in the presence of applied voltage is called reverse biased pn junction diode. Pn junction diode baising and its vi characteristics. 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, lightemitting diode led, laser diode, photo detector, or solar cell in electronics. We have also learned about diffusion current, depletion region. A pn junction diode is a twoterminal electronics element, which can be classified as either. This page tells about reverse breakdown in an pn junction diode.
The boundary between the p and the n regions is called the pn junction. Forward biased pn junction diode physics and radio. A pn junction is formed by diffusing a ptype material to an ntype wafer and there are several other ways as well, see your text. This large amount current starts to flow above the knee point in the forward characteristic with the application of a small amount of external potential. This applied reverse voltage establishes an electric field which acts in the same direction as the field due to the potential barrier. The same number of minority carriers are being swept. Note to those familiar with a diode turn on voltage. Due to this characteristic, the diode finds number of applications as given below. Hence, the resultant field at the junction is strengthened and the barrier height is increased as shown in the above figure. Silicon a single silicon atom consists of fourteen negatively.
To find cutin voltage for silicon pn junction diode. However, unlike a resistor, a diode does not behave linearly with respect to the applied voltage as the diode has an exponential currentvoltage. Hence, very small electric current flows in the pn junction diode. This nonlinear characteristic illustrates that during the operation of the n junction, the resistance is not constant. The pn junction is a junction formed together by ptype semiconductor and ntype semiconductor material. Jan 04, 2020 a pn junction is the simplest form of the semiconductor diode. Questions you should be able to answer by the end of todays lecture. A pn junction is the metallurgical boundary between the n and pregions of a semiconductor crystal. The word diode can be explained as di means two and ode is obtained from electrode. Mobile electrons of pside of the pn junction diode constitute. It has a particular voltage known as break down voltage, at which the diode break downs while reverse biased. The pn junction is the root for semiconductor diodes. There are two ways in which we can bias a pn junction diode.
The anode which is the positive terminal of a diode is represented with a and the cathode. This page of application notes section covers pn junction diode applications. The symbol of the diode and the corresponding arrangement of the p and n regions is shown on figure 3b. The direction of external voltage applied in reverse bias is opposite to that of external voltage applied in forward bias. At this condition, due to the attraction of positive terminal of source, electrons which participated in covalent bond creations in ptype material, will be. If you have done upto this, the forward bias circuit of pn. 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. If reverse bias is made too high, the current through pn junction increases abruptly and the voltage at which this phenomenon occurs is called breakdown.
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. Why does the pn junction diode exhibit current rec tification. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction. Pn junction diode and characteristics of pn junction diode. When the pn junction is forward biased the sequence of events that take place are diffusion, drift and recombination. In forward biasing of pn junction the positive terminal of the battery is connected with the ptype material and negative terminal of the battery is connected with the ntype material, hence this configuration is.
The symbols for diodes and transistors use arrows to indi cate the direction that conventional current can flow. When a pn junction is reversed biased it allows very small current to flow through it. In this type of diode, we dope one side of a semiconductor piece with an acceptor impurity and another side with a donor impurity. The actual potential difference across the junction or diode is kept constant by the action of the depletion layer at approximately 0. One of the most common applications of the diode is the pn junction. The pn junction diode is the basic semiconductor diode format. Since a junction forms between a p type and n type material it is called as pn junction. Conventional current flows from positive to negative. Najmabadi, ece65, winter 2012 high concentration of h on the p side holes diffuse towards the junction high concentration of e on the n side electrons diffuse towards the junction n side is positively charged because it has lost electrons. P type and n type semiconductors, takenseparately are of very limited use. It is the most essential and the basic building block of the electronic device. When an external voltage source is applied to pn junction diode, it is called diode biasing. Pn junction diode and diode characteristics electronicstutorials. The width of depletion region decreases with increase in forward bias.
These materials are ntype, having electrons are majority carrier and ptype material, having holes are majority carrier. The junction plays an important role in the development of the diode which is the building block of most of the semiconductor devices like transistors, bjts, solar cells and integrated circuits. The most common type of semiconductor diode is the silicon diode. Forward bias current flows reverse bias no current flow.
Pn junction lab free to use on allows simulation and study of a pn junction diode with different doping and materials. A pn junction diode is said to be forward biased if its ptype is connected to positive. 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. Why does the junction current in forward bias increase. The name diode is derived from diode which means a device that has two electrodes. Biasing means applying external voltages to the device, biasing of a pn junction diode is of two types.
A reverse biased pn junction diode acts like an open switch and blocks the flow of current from anode to cathode. The other differences between the pn junction and zener diode are explained below in the comparison chart. Pn junction tutorial introduction to pn junction diodes. Pn junction underbiasing 14 boltzmanns approximation. Forward biasing a pn junction diode is very simple. 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. Calculate the ideal diode current assuming that the ntype region is much smaller than the diffusion length with w n 1 mm and assuming a long ptype region. A pn junction is a boundary or interface between two types of semiconductor materials, ptype and ntype, inside a single crystal of semiconductor.
This video derives a the vi characteristic of a pn junction diode by means of band diagram analysis. A pn junction diode is formed by doping one side of a piece of silicon with a ptype dopant boran and the other side with a ntype dopant phosphorus. A pn junction with open terminals excluding minority carriers f. Definition, symbol, and types of diodes electrical4u. It is acting as normal diode while forward biasing. The potential at terminal x with respect to y will vary as a sine function with time. Dc diode model to define the dc diode model, we look at the characteristics of an ideal diode and the modifications that were required due to practical considerations. Kasap, 1990 2001 an ebooklet 5 to calculate the forward current when v 0. 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. The basic difference between a forward bias and reverse bias is in the direction of applying external voltage. When the diode is forwardbiased, it can be used in led lighting applications.
260 57 1089 629 570 1393 706 1396 1250 420 434 430 1076 307 749 1504 724 979 1389 265 248 664 249 1136 1004 30 325 1494 895 249 252 621 1354 26 1302