The ideality factor of a diode is a measure of how closely the diode follows the ideal diode. Spice diode and bjt models imperial college london. What is the physical meaning of diode ideality factor in. In this study, a quick and easy method to determine these two parameters by measuring opencircuit, v oc, and shortcircuit current, i sc, is presented. In traditional solar cells, the dominant chargecarrier recombination mechanism can be estimated from currentvoltage characteristics. However, diodes may not be ideal due to many different reasons. The detailed theory of the pn junction diode gives an ideality factor of one for if the current is limited by the recombination of minority carriers in the neutral region and n2 fro the. And the ideality factor, n, can be used to describe this characteristic. On the ideality factor of the radiative recombination.
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. Rises above 1 if there is significant recombination of carriers in the depletion layer. Understanding of the operation of the zener diodes. A relation is derived for the effective ideality factor by taking into account all junctions of the diode structure. The turn on voltage of a schottky diode is typically smaller than a comparable pn junction since the barrier to forward current flow m s is typically small. Doping dependence of the barrier height and ideality.
The measurement of i 0 is only valid when the ideality factor is stable. Diode spice model dc equivalent circuit used for spice. As you know ideality factor defines how good your diode is. The parameter n is an ideality factor for the diode, known as the emission coefficient. Imax and imelt specify the pn junction explosion current expli which is used in the following equations. The experiment found the silicon diode to have an ideality factor of 1 and the germanium to have a factor of 1. This is a complex way of saying that current increases a factor of 10 for every x mv change in. Extraction of saturation current and ideality factor from. The name diode is derived from diode which means a device that has two electrodes.
Likewise, different voltage v 2 across this same diode a diode of course results in a different current i 2. The fudge factor n is called the diode ideality factor. Pdf modeling the lowvoltage regime of organic diodes. When the pn junction diode in figure 1 is forward biased, the builtin potential barrier is lowered. Using that assumption the derivation produces the ideal diode equation below and the ideality factor, n, is equal to one. Krupanidhia amaterialsresearchcentre,indianinstituteofscience,bangalore560012,india bcentralresearchlaboratory,bharatelectronics,bangalore5600,india received 18 october 1999. The ideality factor of a diode is a measure of how closely the diode follows the ideal diode equation. Diode ideality factor in modern lightemitting diodes. Ideality factor in transport theory of schottky barrier diodes arxiv. Now, it depends on i, v, temperature and junction quality. Kasap, 1990 2001 an ebooklet 3 in this way from the neural regions.
Tunnel diodes esaki diode tunnel diode is the pn junction device that exhibits negative resistance. The diode law for silicon current changes with voltage and temperature. The ideality factor of the gan pn junction was calculated from the iv curve to be n 8. Iisate qvankt 6 where n is called the ideality factor and is a number somewhere between 1 and 2. The processor core thermal diode ideality factor the thermal diode is on the processor core of the pentium ii xeon processor.
Silicon a single silicon atom consists of fourteen negatively. That means when the voltage is increased the current through it decreases. It has a spice parameter called n all spice parameters are given in capitals. The ideal diode equation makes a number of assumptions. Develop an understanding of the pn junction diode and its behavior. Index terms schottky barrier, iv characteristics, ideality factor, quantum. Physica b 307 2001 1257 doping dependence of the barrier height and ideality factor of aungaas schottky diodes at low temperatures m. Deviations in the ideality factor from one indicate that either there are unusual recombination mechanisms taking place or that the recombination is changing in magnitude.
Video created by georgia institute of technology for the course introduction to electronics. The ideality factor also called the emissivity factor is a fitting parameter that describes how closely the diodes behavior matches that predicted by theory, which assumes the pn junction of the diode is an infinite plane and no recombination occurs within the spacecharge region. The ideal diode characteristic equation is known as the shockley equation, or simply the diode equation. Pdf ap831 ap831 pn junction diode ideality factor silicon diode ideality factor pentium ii xeon single edge contact s. Colloidal quantum dot active layers for light emitting diodes. A pn junction diode is formed when a ptype semiconductor is fused to an ntype semiconductor creating a potential barrier voltage across the diode junction the effect described in the previous tutorial is achieved without any external voltage being applied to the actual pn junction resulting in the junction being in a state of equilibrium. Exact analytical solution of the diode ideality factor of a pn junction.
At room temperature, higher value of ideality factor means the junction. For a perfect pnjunction, the recombination mechanism can be approximated by the ideality factor. The equation used to model this non ideal behavior is. Recombination dominated diode behavior in general, a particular diode might have a combination of these two effects going on, and so people often use a more general form for the diode equation. Pn junction diode 7 diode equation where i s reverse saturation current a v d voltage applied to diode v q electronic charge 1. Pdf exact analytical solution of the diode ideality factor of a pn. According to my professor the ideality factor is indicative of the type of charge carrier recombination that is occurring inside of the diode based on the following chart. The vi characteristics of the ideal diode are shown in the figure below. The properly called shockley equation has the non ideality factor n. An ideal pn junction diode is based on the following basic assumption.
The shockley diode equation or the diode law, named after transistor coinventor william shockley of bell telephone laboratories, gives the iv currentvoltage characteristic of an idealized diode in either forward or reverse bias applied voltage. The ideality factor of the pn junction will follow the sahnoyceshockley model and yield an ideality factor between n 1 and n 2. A pn junction is the simplest form of the semiconductor diode. A study on the electrical characteristic analysis of csi solar cell diodes pyungho choi, hyojung kim, dohyun baek, and byoungdeog choi. What is the lowest ideality coefficient of the schottky. Compensating for ideality factor and series resistance. A diode has a characteristic semi logarithmic slope which describes the multiple of the current obtained for an incremental linear change in potential. Similarly, when the diode is reversed biased, it acts as a perfect insulator with zero current through it. Near unity ideality factor and shockleyreadhall lifetime. Understanding of the operation of biased pn junction rectifier diodes 2.
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. Extraction of saturation current and ideality factor from measuring. The origin of the high diode ideality factors in gainngan multiple quantum well lightemitting diodes di zhu,1 jiuru xu,1 ahmed n. We will address more about the ideality factor later as we modify the ideal diode equation.
Saturation current i 0 and ideality factor n of a p n junction solar cell are an indication of the quality of the cell. A study on the electrical characteristic analysis of csi. Semiconductor physics lab, faculty of physics, moldova state university, 60 a. The residual value of ideality factor can then be attributed to the metal semiconductor junction. The width of the depletion region with a reverse bias v. What is the physical significance of ideality factor in. 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. The origin of the high diodeideality factors in gainngan.
An abrupt silicon pn junction n a 10 16 cm3 and n d 4 x 10 16 cm3 is biased with v a 0. Maximum deviation of a particular diode from ideal behavior is represented by an ideality factor. The ideal diode equation assumes that all the recombination occurs via band to band or recombination via traps in the bulk areas from the device i. Stated differently, there is a reverse current due to the diffusion of minority carriers in neutral regions towards the scl. A pn junction diode is a kind of semiconductor diode that made up of a joining ptype and ntype semiconducting layers. The ideality factor of silicon and germanium physics forums. If model parameter allowscaling is set to yes, the diode geometry parameters periph, width, and length are multiplied by scale, while area is multiplied by scale scale for level 11 only. We often use the ideal diode equation in the form of. The current in the pn junction diode can only flow from one side to the other. Nonideal pn junction diodes engineering libretexts.
The scratches with 9g and 27 g load generated a further increase both of the recombination. These two parameters are usually estimated from dark currentvoltage measurements. Measurements and analysis of currentvoltage characteristic of a pn. The sahnoyceshockley sns analysis gave a physical meaning to the ideality factor 1, 2. A relation is derived for the effective ideality factor by taking into. The jv curve is often treated as an ideal diode described by the shockley equation. The pn junction is the fundamental building block of the electronic age. Thus the ideality factor is a powerful tool for examining the recombination in a device. The model uses the solar radiation g t, the ambient temperature t a t at the panel surface, and the pvp parameters, to evaluate the pv current i c t of one pv cell see. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of 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. In practice, there are second order effects so that the diode does not follow the simple diode equation and the ideality factor provides a way of describing them. Pdf the paper presents a new analytical method for extracting the diode ideality factor of a pn junction device using lambert wfunction. A diode is said to be an ideal diode when it is forward biased and acts like a perfect conductor, with zero voltage across it. The diode ideality factor has been subjected to theoretical discussions from the viewpoint of lightemitting diodes leds. Forward biasing a pn junction diode is very simple.
A study on the electrical characteristic analysis of csi solar cell diodes parameter vbi. As radiative recombination in leds is incongruent with the sahnoyceshockley sns analysis, the sns recombination plane was replaced with carrier. Definition, symbol, and types of diodes electrical4u. For a perfect pn junction, the recombination mechanism can be approximated by the ideality factor. 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.
Since the reverse saturation current, is is typically very small 109 to 1015 a, the expression. Diodes fabricated from a bulk gan pn junction and a pnjunction structure with a ptype algangan superlattice display ideality factors of. The paper presents a new analytical method for extracting the diode ideality factor of a pn junction device using lambert wfunction model and the dark current. But then a number of texts suggest that ideality factor is a guide to the efficiency of a diode detector eg ben ben tongues paper. The derivation of the simple diode equation uses certain assumption about the cell. Exact analytical solution of the diode ideality factor of. Esaki diodes was named after leo esaki, who in 1973 received the nobel prize in physics for discovering the electron tunneling effect used in these diodes.
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. Diode spice model ideality factor accounts for generationrecombination in the depletion region of the diode ignored in our derivation for id usual range for n is 0. The junction of n and p semiconductors is free of charge carriers. The scratch with 6 g load clearly increased the forward current and the ideality factor, but the ideality factor did not exceed n 2. The pn junction diode is the most fundamental of all. Ee105 fall 2014 microelectronic devices and circuits. Figure 5 depicts the real diode iv characteristic for a fairly typical silicon diode for positive diode voltages.
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