The operation of actual solar cells is typically treated as a modification to the basic ideal diode equation described here. Light intensity and photon flux photogeneration in silicon. General solution for wide base pn junction overview situation where the solar cell surface is far enough away from the junction edges that recombination properties of carriers injected into the quasineutral region under forward bias are not impacted. Unipolar transistors, such as fieldeffect transistors, use only one kind of charge carrier. Current hole diffusion current negligible due to large energy barrier hole drift current current flow is constant due to thermally generated carriers swept out by efields in the depletion region current flow is dominated by minority carriers flowing across the junction and becoming majority carriers quicktime movie. Of course, we can just give you the equation to figure it out, but what good will that do. Diode current equation expresses the relationship between the current flowing through the diode as a function of the voltage applied across it. For the next part of derivation we are shifting to the second coordinate system shown in. Typical iv static characteristics of a silicon pn junction diode. Apr 16, 2009 i am looking for the simplest possible derivation of the diode equation.
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. In this lecture, the educator has discussed how to derive a diode current equation in forward bias and. Index termsbipolar junction transistor bjt, diode current. The equation 2 can be written for open circuited unbiased pn junction diode by putting v 0 as. The current in a pn diode is due to carrier recombination or generation somewhere within the pn diode structure. Solve for the carrier concentration and current in the quasineutral regions regions i and iii on the diagram under. The current voltage function also called the iv characteristic for an ideal diode is.
The higher the rate of recombination events, the greater the current which flows across the junction. Let us study the derivation of the mathematical expression for the current through a diode, which gives its vi characteristics. The default pn junction device geometry we use in our analyses, including two alternative. Shockley derives an equation for the voltage across a pn junction in a long article published in 1949. Jan 28, 2017 i is current flowing through the diode. Pn junction diode parameters like reverse saturation current, bias current, reverse breakdown voltage and barrier voltage are dependent on temperature. Characteristics of junction diodes technical articles. Space charge region an overview sciencedirect topics. Diode current equation vi characteristics of pn junction diodeapplication half wave rectifier and full wave rectifiers with and without filters derivation of ripple. Pn junction diode derivation of junction resistance junction breakdown. Ec8252 electronic devices ed regulation 2017 unit i semiconductor diode. It is a semiconductor device and it comes in two general types. I am looking for the simplest possible derivation of the diode equation.
To see how it can be derived, we must examine the various reasons for current. The pn junction and the diode effect, current in the diode, the pn diode as a circuit element, circuit applications of ordinary diodes, power supplies, power supply filtering, split power supply, diode gate, diode protection. Hence from equation we conclude that the current should decrease with increase in. 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. The current is much increased by reducing the base widths for fixed diffusion lengths.
Diode circuits tutorial pdf 25p this note covers the following topics. A small increase in the drift current is experienced due to the small increase in the width of the depletion region. The junction can be formed by the implantation or diffusion of dopants in an wafer. The saturation current is proportional to n i 2, and thus increases exponentially with either increasing temperature or reductions in band gap. May 16, 2015 this feature is not available right now. Module 1 semiconductor pnjunction diodes what are they and what is their purpose. Assume that the forward current is determined by the shockley equation minority carrier diffusion. In this type of diode, we dope one side of a semiconductor piece with an acceptor impurity and another side with a donor impurity. Pn junction diode 1 ee105 fall 2014 microelectronic devices and circuits prof. Diodes are electronic check valves which allow current to flow freely in one direction, but block current flow in the opposite direction.
As long as the light is on, there is a current flowing through the pn junction. Diffusion current is a current in a semiconductor caused by the diffusion of charge carriers holes andor electrons. Later he gives a corresponding equation for current as a function of voltage under additional assumptions, which is the equation we. The shockley ideal diode equation characterizes the current across a pn junction as a function of external voltage and ambient conditions temperature, choice of semiconductor, etc. Light intensity and photon flux photogeneration in silicon photodiode basic operation photocurrent derivation. A diode with a larger recombination will have a larger i 0.
The use of the diode equation in circuit problems is illustrated in the article on diode modeling. The short circuit current, i sc, is the current at zero voltage which equals i. At thermal equilibrium 1 number of carriers in the. As seen in the previous sections, a pn junction diode creates the following current. Lecture 5lecture 5 pn junction diodes quantitative. Feb 09, 2009 the forward conduction vi characteristics are similar between a zener diode and a regular pn junction diode. The equation for the diode current of a planeparallel junction diode 2 is i is exp 1 kt where is is the saturation current of the diode, q is the electronic charge, k is boltzmanns constant, and t is the junction temperature in k. In this video i will derive the ideal diode equation which involves deriving the minority carrier concentration as a function of depth into the depletion region.
In a pn junction, 2 regions having no electric field are on the ends of the device and are termed quasineutral regions. Hence from equation we conclude that the current should decrease with increase in temperature but exactly. Derivation of vi characteristics of pn junction diode 4. The slope of the pn junction diode in forwarding bias shows the resistance is very low. Solve minority carrier diffusion equation in quasineutral regions determine minority carrier currents from continuity equation evaluate currents at the depletion region edges add these together and multiply by ar ea to determine the total current through the device. As in forward bias, the drift current is limited by the number of minority carriers on either side of the pn junction and is relatively unchanged by the increased electric field. Rajiv gandhi college of engineering and technology itt32 electronic devices and circuit uniti diode current equation vi characteristics of pn junction diode application half wave rectifier and full wave rectifiers with and without filters derivation of ripple factor rectification of efficiency and tufzener diode and.
Theory of pn junction diode, diode current equation. Forward current derivation through diode this is the derivation of current through the diode considering minority charge carriers concentration in n region that is holes and minority charge. Lecture 5lecture 5 pn junction diodes quantitative analysis. How to derive forward current equation for pn junction.
The forward biased iv characteristics of real pn diodes are further affected by high injection and the series resistance of the diode. One of the results produces rectification as seen in the pn junction diodes static iv currentvoltage characteristics. Pn junction diode is widely known for passing the electric current solely in one direction. The diode equation gives an expression for the current through a diode as a function of voltage. Dec 08, 2017 in this lecture, the educator has discussed how to derive a diode current equation in forward bias and reverse bias.
Ee105 fall 2014 microelectronic devices and circuits. First,the poisson equation describing the band bending in the depletion. If ri rl the diode reverse current and voltage equations can be simplified using rl 0. Module 2 essentially, they serve the same function in circuits, as the valves in your heart and. The vi characteristics of pn junction diode in forwarding bias are nonlinear, that is, not a straight line. I need it to reference to it in my advanced higher project. Band diagrams and builtin voltage of the pn junction. Here we will describe the system characteristics of the bjt. The heterojunction pn diode is in principle very similar to a homojunction. What is usually done is to measure the diode current and forward voltage over several orders of magnitude of current. Gupta assistant professor department of electronics engineering shri ramdeobaba college of engineering and management, nagpur. When the diode is forwardbiased, it can be used in led lighting applications. Pn junction diode, current equations, energy band diagram, diffusion and drift current densities, forward and reverse bias characteristics, transition and diffusion capacitances, switching characteristics, breakdown in pn junction diodes. For discrete diodes, the reverse saturation current is usually at i s 10 na.
This recombination can occur within the quasineutral regions, within the depletion region or at the metalsemiconductor ohmic contacts. This value is proportional to the crosssectional area of the pn junction. It is one of the simplest semiconductor devices as it allows current to flow in only one direction. Therefore, for pnjunctions in ics, the reverse saturation current is much lower.
Semiconductor energy bands and fermi energy concept free electrons free holes valence band. From this equation, we have a relation between the circuit current it and the electron. It would me consistent with the diode current equation idisexpvdnvt1, cause in 0. Under forward bias, the diode current is due to recombination. The amount of current flowing through the pn junction diode greatly depends on the type of material used and also depends on the concentration of doping in the fabrication of pn diode. A cert ain pn junction diode has a leakage current of 10. A pn junction diode is a twoterminal electronics element, which can be classified as either. Device physics i pn junctions diode equation neudeck p. Bipolar junction transistors bjt general configuration and definitions the transistor is the main building block element of 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. Just as for the homojunction we find that current in a n junction can only exist if there is recombination orp generation of electron and holes somewhere throughout the structure. A pn junction diode is designed to have a relatively high reverse breakdown voltage while a zener diode is designed to have a specific breakdown voltage within a relatively narrow band of. Junction field effect transistor jfet the single channel junction fieldeffect transistor jfet is probably the simplest transistor available. There are two distinct bias conditions for a pn junction diode.
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. 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. A bipolar transistor allows a small current injected at one of its terminals to control a much larger current flowing between two other terminals, making the. The dark saturation current i 0 is an extremely important parameter which differentiates one diode from another. This is the basic construction of the pn junction diode. Pn junction diodes quantitative analysis math, math and more math georgia tech ece 4833.
Pn junction diode 2 diode introduction a diode is formed by joining an ntype semiconductor with a ptype semiconductor. The derivation of the ideal diode equation is covered in many textbooks. There are a few basic concepts to be introduced, such as energy bands, drift and diffusion currents, etc. Using approximate boltzmanns diode equation, find the change in forward bias. The treatment here is particularly applicable to photovoltaics and uses the concepts introduced earlier in this chapter.
Vi characteristics of pn junction diode in 3biasing modes. P type and n type semiconductors, takenseparately are of very limited use. Simple derivation of diode equation physics forums. Likewise, we can find the voltage across the diode. A bipolar junction transistor bipolar transistor or bjt is a type of transistor that uses both electrons and holes as charge carriers. This pn junction can be used to operate and implement the functions of a diode because it can conduct considerable current in the forward direction and roughly no current in the reverse direction. The potential barrier in the pn junction diode is the barrier in which the charge requires additional force for crossing the region. Alan doolittle pn junction iv characteristics electron diffusion current electron drift current hole diffusion. Lets now get back to the equilibrium condition and start to analyze the junction quantitatively. Short table of contents list of figures, list of tables title page table of contents. Pn junction diode baising and its vi characteristics. Most semiconductor devices involve regions with two different kinds of doping, so a pn junction is present in all of them. Lets consider the bandbending and carrier densities at equilibrium.
The basis for derivation of the equation of the depletion region vi characteristic are the. 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. This nonlinear characteristic illustrates that during the operation of the n junction, the resistance is not constant. One of the most common applications of the diode is the pn junction.
The diode current equation presented in equation 3. Electronics tutorial about the pn junction diode and the vi characteristics of pn. Pdf a new derivation of the law of the junctions researchgate. In other words, the barrier in which the charge carrier stopped by the obstructive force is known as the potential barrier. Application of the current continuity equation dx o p n n n. Applying the basic equations to a pn junction pveducation.
I unfortunately dont know how to derive it and i cant find one simple enough to use. If the reverse bias saturation current is taken to be i. V applied voltage across the terminals of the diode. In this lecture, the educator has discussed how to derive a diode current equation in forward bias and reverse bias. The diode does not behave linearly with respect to the applied voltage, and it has an exponential vi relationship. Pn junction diode and characteristics of pn junction diode. Derivation of vi characteristics of pn junction diode.
Ec8252 electronic devices ed regulation 2017 semester 2. Explain the effect of temperature on pn junction diode. This is the current which is due to the transport of charges occurring because of nonuniform concentration of charged particles in a semiconductor. Diode characteristics dynamic resistance, transition time. The main problem that needs to be tackled is the effect of the bandgap discontinuities and the different material parameters, which make the actual calculations more complex even though the pn diode concepts need almost no changing. I 0 dark saturation current, the diode leakage current density in the absence of light. We use them when we need current to flow in only one direction.
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