In this tutorial, we will learn about pn junction diodes and in particular the characteristics and working of pn junction diode. The current in the pn junction diode can only flow from one side to the other. What are the depletion width in the nregion, the depletion width in the pregion, and the builtin potential at 300k. Pn junctions consist of two semiconductor regions of opposite type. In solar cell applications, optical illumination is steady, and dc current i. A pn junction diode is a twoterminal electronics element, which can be classified as either step graded or linear graded.
In realistic settings, current will deviate slightly from this ideal case. Lecture 5lecture 5 pn junction diodes quantitative. No generationrecombination in the depletion layer 6. Apr 23, 2020 the ideal diode equation is an equation that represents current flow through an ideal p n junction diode as a function of applied voltage.
Pn junction diode is one of the fundamental elements in electronics. In this type of diode, we dope one side of a semiconductor piece with an acceptor impurity and another side with a donor impurity. May 16, 2015 for the love of physics walter lewin may 16, 2011 duration. A diode is a simple device, which can be implemented by a pnjunction, as well as other heterojunction structures. What happens when we join ptype and ntype semiconductors.
The main characteristic of a pnjunction or a diode is that for positive voltages forward bias the diode is conduction, whereas for negative voltages reverse bias the current flow is blocked. Simple derivation of diode equation physics forums. Assume that the forward current is determined by the shockley equation minority carrier diffusion. To plot voltampere characteristics of silicon pn junction diode. Semiconductor pnjunction diodes physically, diodes are formed by the interface between two regions of oppositely doped semiconductor i. Diode current equation vi characteristics of pn junction diodeapplication half wave rectifier and full wave rectifiers with and without filters derivation of ripple. It is followed by the modelname that will be used by diode components to refer to the model. The junction can be formed by the implantation or diffusion of dopants in an wafer. I 0 is directly related to recombination, and thus, inversely related to material quality nonideal diodes include an n term in the denominator of the exponent. Iv characteristics qthe ideal diode equation qualitative derivation uequilibrium situation uthe ivcharacteristics of the ideal diode are modeled by the ideal. An ideal pn junction diode is based on the following basic assumption.
A pn junction is the metallurgical boundary between the n and pregions of a semiconductor crystal. As we said,i is a very small current, and so trying to do the reverse test is probably not going to be successful. Such junctions show a pronounced rectifying behavior. Apr 05, 2019 in this tutorial, we will learn about pn junction diodes and in particular the characteristics and working of pn junction diode. Lecture 5lecture 5 pn junction diodes quantitative analysis. I am looking for the simplest possible derivation of the diode equation. A pn junction diode is a twoterminal electronics element, which can be classified as either. One thing you might ask yourself is how could i check to see if an actual diode follows the equation given sathere. The goal is to extract power from the cell, and the iv characteristics are plotted in terms of cell current and cell voltage. Basic diode electronics introduction to diodes the pn junction the pn junction is a homojunction between a ptype and an ntype semiconductor.
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. Shockley derives an equation for the voltage across a pn junction in a long article published in 1949. Pn junction diodes quantitative analysis math, math and more math. The ideal diode characteristic equation is known as the shockley equation, or. The following equation is called the shockley ideal diode equation when n, the ideality factor, is set equal to 1.
Applying the basic equations to a pn junction pveducation. Reverse diode leakage is related to offstate leakage of an ic current proportional to the diode junction area and inversely proportional to doping why you want lightly doped substrates reverse current dependent on the. In this lecture, the educator has discussed how to derive a diode current equation in forward bias and reverse bias. Later he gives a corresponding equation for current as a function of voltage under additional assumptions, which is the equation we call the shockley ideal diode equation. Mathematically it is given as where, i is the current flowing through the diode i0 is the dark saturation current, q is the charge on the electron, v. Likewise, different voltage v 2 across this same diode a diode of course results in a different current i 2. The pn junction is the fundamental building block of the electronic age. Furthermore, an equivalent circuit for pnjunctions will be presented. The ideal diode equation is an equation that represents current flow through an ideal pn junction diode as a function of applied voltage. Lecture 15 the pn junction diode i iv characteristics november.
Typical iv static characteristics of a silicon pn junction diode. Pn junction diode 14 photo diodes and photodetectors if the depletion region of a pn junction diode is illuminated. In realistic settings, current will deviate slightly from. Abrupt depletion layer approximation let apply bias and calculate current through the pn junction currents in pn junction from sze, 1981. The diode equation gives an expression for the current through a diode as a function of voltage. A silicon pn junction na 1016 cm3 and n d 4 x 1016 cm3 is biased with v a 3 v. We use them when we need current to flow in only one direction. It applies the minority carrier diffusion equations to the pn junction to arrive at the idea. The shockley ideal diode equation or the diode law named after the bipolar junction transistor coinventor william bradford shockley gives the iv characteristic of an ideal diode in either forward or reverse bias or no bias. Jan 29, 2019 pn junction diode is one of the fundamental elements in electronics. The pn junction diode ii equivalent circuit model november 3, 2005. Pn junction underbiasing 14 boltzmanns approximation.
This understanding will lay a better foundation for exploring further into different aspects of semiconductor electronics. Pn junction diode 1 ee105 fall 2014 microelectronic devices and circuits prof. Low injection fermi level do not change in the depletion layer minority carrier densities p. 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.
Similar to the resistance value r of a resistor, or the capacitance c of a capacitor, these three parameters specify the performance of a junction diode. Semiconductor pn junction diodes physically, diodes are formed by the interface between two regions of oppositely doped semiconductor i. Questions you should be able to answer by the end of todays lecture. According to this assumption, the device can then be broken up into regions that have an electric field and those that do not. I 0 dark saturation current, the diode leakage current density in the absence of light. The pn junction forms the basis of the semiconductor diode. N is the ideality factor, ranging from 12, that increases with decreasing current. 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 equation 2 can be written for open circuited unbiased pn junction diode by putting v 0 as, where p n0 is the concentration of holes on nside just near the junction when diode is open circuited i. A diode is a simple device, which can be implemented by a pn junction, as well as other hetero junction structures. The semiideal diode had a leakage current across the junction the reverse saturation current, shown by i. Pn junction is a significant building block and it is one among the indispensable structures. Most semiconductor devices involve regions with two different kinds of doping, so a pn junction is present in all of them.
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. The ideal diode equation is an equation that represents current flow through an ideal p n junction diode as a function of applied voltage. Pn junction diodes quantitative analysis math, math and more math georgia tech ece 4833. Note to those familiar with a diode turn on voltage. From the above, it follows that zero power dissipation occurs in an ideal diode. I need it to reference to it in my advanced higher project. Jul 30, 2018 diode current equation expresses the relationship between the current flowing through the diode as a function of the voltage applied across it. Physics of semiconductor devices pn junction depletion width problem a silicon pn diode has a doping of n d 81015 1 cm3 and n a 210 16 1 cm3. It acts as a diode, which can serve in electronics as a rectifier, logic gate, voltage regulator zener diode.
Diode current equation expresses the relationship between the current flowing through the diode as a function of the voltage applied across it. However, unlike a resistor, a diode does not behave linearly with respect to the applied voltage as the diode has an exponential currentvoltage. Uniti diode current equation vi characteristics of pn junction. There are a few basic concepts to be introduced, such as energy bands, drift and diffusion currents, etc. Apr 23, 2020 a pn junction diode is a kind of semiconductor diode that made up of a joining ptype and ntype semiconducting layers. In this equation, two parameters require to be discussed in quite detail. This means the barrier will increase instead of decrease, and so we have what is shown in figure 1. 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. Physics of semiconductor devices pn junction depletion. V applied voltage across the terminals of the diode. Ee105 fall 2014 microelectronic devices and circuits.
For the love of physics walter lewin may 16, 2011 duration. At the point of the junction, which we call the metallurgical junction, is where n d n a 0. Pn junctions and the diode equation photovoltaic solar. There is also a difference in the reverse bias region due to both material characteristics and fabrication of the diode junction. Dec 08, 2017 in this lecture, the educator has discussed how to derive a diode current equation in forward bias and reverse bias. A pn junction diode is a kind of semiconductor diode that made up of a joining ptype and ntype semiconducting layers. Silicon a single silicon atom consists of fourteen negatively. It applies the minority carrier diffusion equations to. The applied electric field nowadds in the same direction to the builtin field. Kasap, 1990 2001 an ebooklet 4 d what is the reverse current at 27 c when the diode voltage is. The electric field distribution is defined by poissons equation. 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. Of course, we can just give you the equation to figure it out, but what good will that do.
The rest of the model contains pairs of model parameters and values, separated. Physics of semiconductor devices pn junction depletion width. Derivation of vi characteristics of pn junction diode. Nonideal pn junction diodes engineering libretexts. Calculate the builtin potential, the depletion layer width and. I unfortunately dont know how to derive it and i cant find one simple enough to use.
Reverse saturation current in a silicon pn junction diode nearly doubles for very a. The diode equation the reason for calling the proportionality constant isat will become obvious when we consider reverse bias. Likewise, we can find the voltage across the diode. The same number continuously recombine at ohmic contact. Pn junction diode 2 diode introduction a diode is formed by joining an ntype semiconductor with a ptype semiconductor. Pn junction diode in the reversebiased configuration is sensitive to light from a range between 400nm to nm, which includes visible light. Pn junction diode baising and its vi characteristics. Cuevas, the recombination parameter j0, energy procedia, vol. Device physics i pn junctions diode equation neudeck p. The voltampere characteristics of a diode explained by following equation. As seen in the previous sections, a p n junction diode creates the following current. A builtin potential also exists at a junction between a metal and a.
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