Electronic devices ed ee8252 notes pdf free download. Unit i semiconductor diode ec8252 electronic devices notes. Any applied voltage must therefore drop across the scl. The energy band diagram of the ntype semiconductor and metal is shown in the below figure.
Zero bias no external voltage potential is applied to the pn junction diode. Biasing the pn junction the diode trouble shooting. Some electrons elevated to conduction band by thermal energy. Dec 27, 2017 this video provides knowledge on how to draw the energy band diagran for a pn junction. Energy band diagram at thermal equilibrium at thermal equilibrium energy band diagram of a pn junction in thermal equilibrium while in thermal equilibrium no external voltage is applied between the ntype and ptype material, there is an internal potential, f, which is caused by the workfunction difference between the ntype and ptype pn. The second theory of reverse breakdown effect in diodes is known as avalanche breakdown and occurs at reverse voltages beyond 5 volts. Pn and metalsemiconductor junctions higher education.
The forwardbias and the reversebias properties of the pn junction imply that it can be used as a diode. Draw the energy level diagram of a pn junction and explain how a junction barrier is developed across an unbiased junction. When an open circuit solar cell is illuminated, the light generated electrons and holes. A pn junction consists of two semiconductor regions with opposite doping type as. The pn junction is an electrical diode, a device through which. If a pn junction has an external forward bias voltage applied across it, a current will flow through the junction of the solar cell from the ptype side to the ntype side conventional current. Smith department of eecs university of california, berkeley eecs 105 spring 2004, lecture 19 prof. A pn junction is a boundary or interface between two types of semiconductor materials, ptype. Unlike the ordinary pn junction diode, the difference in energy levels is very high in tunnel diode. It acts as a diode, which can serve in electronics as a rectifier, logic gate, voltage regulator zener diode. Schottky diode definition, symbol, working and applications.
Semiconductors pn junction theory questions and answers pdf free download for electronics engineering students,mcqs,objective questions viva. A pn junction diode allows electric charges to flow in one direction, but not in the opposite direction. In solidstate physics of semiconductors, a band diagram is a diagram plotting various key electron energy levels fermi level and nearby energy band edges as a function of some spatial dimension, which is often denoted x. Semiconductor, silicon, pn junction, forward bias, reverse bias, diode. The pn junction diode may get destroyed due to excessive heat if any of these values are exceeded. Draw the energy band diagram of pn junction diode in forward. Therefore, when the fermi level of the semiconductor, e fs, is aligned with the fermi level of the gate, e fm, there is no band bending in any region of the mos capacitor. Energy band gap kit containing a pn junction diode placed.
Draw the energy band diagram of pn junction diode in forward and reverse bias condition. From the above, it follows that zero power dissipation occurs in an ideal diode. Step pn junction energy band diagram physics forums. These diagrams help to explain the operation of many kinds of semiconductor devices and to visualize how bands change with position band bending. 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. Energy band diagram for a pure intrinsic silicon crystal with unexcited atoms. This understanding will lay a better foundation for exploring further into different aspects of semiconductor electronics.
Oct 05, 2017 in this lecture, i discussed about the energy band diagram of the pn junction in equilibrium. As you can see, the valence and conduction bands in the n region are at lower energy levels than those in the p region, but there is a significant amount of overlapping. Note to those familiar with a diode turn on voltage. It does not correspond to any physical spatial bending. Energy band diagram of a pn junction a before and b after merging the ntype and ptype regions note that this does not automatically align the fermi energies, e f,n and e f,p. The pn junction biasing the pn junction the diode trouble shooting. State of diode is unknown before solving the circuit 1. Energy band diagram of a pn junction under reverse and forward bias pnjuntiondiode.
Write down all circuit equations and simplify as much as. Energy band diagram an overview sciencedirect topics. As we increase the applied volatge the drop across the nuentral region increases such that the n side depletion region is always higher in. The diode current in a tunnel diode is same as that for normal pn junction diode which is given as i diode i do exp v. This carrier diffusion is identical to that in a pn junction. A diode is a simple device, which can be implemented by a pn junction, as well as other hetero junction structures. We will assume, unless stated otherwise, that the doped regions are uniformly doped and that the transition between the two regions is abrupt.
Electrons and holes reach an equilibrium at the junction and form a depletion region. The metallurgical junction zone has been depleted of carriers compared with the bulk. The panels show energy band diagram, electric field, and net charge density. The energy band diagram of an ideal ptype substrate mos capacitor at zero bias is shown in figure 3. Pn junction diode in the reversebiased configuration is sensitive to light from a range between 400nm to nm, which includes visible light. Draw to scale the energy band diagram of the junction at equilibrium. Heat, light, and other stimuli can excite electrons across the band gap, resulting in. Realise the pn junction behaviour when applying a dcvoltage. The energy band diagram of the pn junction under open circuit conditions is shown in figure 6. The valence band and conduction band in ntype material are slightly lower than that of ptype material. Draw the energy band diagram of pn junction diode in.
The pn junction provides satisfactory performance when operated within these limiting values. 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. Jan 29, 2019 pn junction diode is one of the fundamental elements in electronics. This type of breakdown diode has a depletion region that is deliberately made narrower than the depletion region in the normal pnjunction diode, but thicker than.
A pn junction diode is a twoterminal electronics element, which can be classified as either. Includes details of pn junction operation which is not covered in this course. Problems and solutions to physics of semiconductor. A perfect diode is a device that only allows current to flow through it in one direction, i. Pn junction tutorial introduction to pn junction diodes. There are a few basic concepts to be introduced, such as energy bands, drift and diffusion currents, etc. When the pn junction is forward biased, the electrons in the ntype material which have been elevated to the conduction band and which have diffused across the junction find themselves at a higher energy than the holes in the ptype material. V t1 where i do is reverse saturation current and will be very high in tunnel diode compared to pn junction diode due to high doping concentrations. Electrons near the maxima in valence band have been thermally excited to the empty states near the conductionband minima, leaving behind holes. Pn junction diode is one of the fundamental elements in electronics. The circuit symbol of a pn junction diode is shown in. Figure 7 iv curve of the silicon pn junction diode. When looking at a band diagram, the electron energy states bands in a material can curve up or down near a junction.
Apr 05, 2019 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. Band gap is the energy difference between the top of valance band and the bottom of conduction band for small inter distance. However, electrons in the conduction band of the n region will tunnel to the empty states of the valence band in p region. A diode is a simple device, which can be implemented by a pnjunction, as well as other heterojunction structures. In an ideal mos capacitor, the metal work function. To return the semiconductor to separate pieces, click the separate button or drag one object away from the other. Forward bias current flows reverse bias no current flow. The diode has two terminals called a cathode and an anode. Band diagram of pn junction under a equilibrium and b forward bias.
In a p on n structure, this can be accomplished by inserting an electronblocking unipolar barrier at the junction of the pn diode to form the pbn diode klipstein, 2008. Potential barrier is still very high no noticeable injection and forward current through the junction. See the figure in in band diagram, why the fermi energy ef is constant along the device. To return the semiconductor to separate pieces, click the separate button or drag one object away from th. Tunnel diode definition, symbol, and working diode. Semiconductor pnjunction diodes physically, diodes are formed by the interface between two regions of oppositely doped semiconductor i. The energy band diagram of a quantum well is shown in fig. The energy band diagram of the metal and ntype semiconductor after contact is shown in the below figure. Formation of a pn junction diode and its band diagram. 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. A step pn junction diode is made in silicon with the n side having nd 2x1016 cm3 and the p side having a net doping of na 5x1015 cm3. To determine the energy band gap of a semiconductor by using pn junction diode.
Introduction to diodes advanced energy technology program. Unlike the ordinary pn junction diode, the difference in energy levels. When a pn junction is forward biased then its energy band diagram looks like this. In this lecture, i discussed about the energy band diagram of the pn junction in equilibrium. 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 corresponding energy band diagram is shown in figure 5. Also, note that this flatband diagram is not an equilibrium diagram since both electrons and holes can lower their energy by crossing the junction. Pn junction diode baising and its vi characteristics. That implies that you would have to supply energy to get an electron to go up on the diagram, and supply energy to get a hole to go down. 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. This video provides knowledge on how to draw the energy band diagran for a pn junction. A tunnel diode is a heavily doped pn junction device in which the electric current decreases as the voltage increases. The upward direction in the diagram represents increasing electron energy. The depletion region extends mainly into the pside. The physics of the solar cell sharif university of. Find current densities j at room temperature for a schottky diode ptngaas at. Semiconductor physics semiconductors and diodessemiconductors.
However, what is different is that the electrons can diffuse as minority carriers through the quasineutral base. Schottky diode is a metalsemiconductor junction diode that consumes less power than the pn junction diode. In order to initiate the junction formation, click the formjunction button or mouse drag one object toward the other. An energy diagram for a pn junction at the instant of formation is shown in figure a. Doped semiconductors ntype materials ptype materials diodes and transistors.
Most semiconductor devices involve regions with two different kinds of doping, so a pnjunction is present in all of them. Relationship between band gap and built in potential for pn junction diode in equilibrium. The depletionlayer, energyband diagram, and concentrations on a logarithmic scale of the mobile electrons nx and holes px are shown as. The energy gap between the valence band and conduction band is known as forbidden energy gap.
When the metal is joined with the ntype semiconductor, a device is created known as schottky diode. Cu, ag, au partially filled band full band empty band. Find the builtin voltage, and compare with the value measured off. For a pn junction at equilibrium, the fermi levels match on the two sides of the junctions. Most semiconductor devices involve regions with two different kinds of doping, so a pnjunction. Energy band diagram of a pn junction a before and b after merging the ntype and ptype regions note that this does not automatically align the fermi energies, ef,n and ef,p. Electronic devices ed ee8252 syllabus pdf free download. They readily combine with those holes, making possible a continuous forward current through the junction.
A pnjunction diode is formed when a ptype semiconductor is fused to an ntype semiconductor creating a potential barrier voltage across the diode junction. The vacuum level is defined as the energy level of electrons that are outside the material. Calculate the capacity of the pn junction from the problem 2 if the area of the. Also, note that this flatband diagram is not an equilibrium diagram since both electrons and holes can.
A pn junction diode is a twoterminal electronics element, which can be classified as either step graded or linear graded. Most semiconductor devices involve regions with two different kinds of doping, so a pn junction is present in all of them. Energy band diagram of a pn junction a before and b after. Note that this result is independent of the kinetic energy of the particleit takes no energy to fall downhill. Pn junction diode and characteristics of pn junction diode. The pn junction is used an electronic circuit element. Review, pn junctions, fermi levels, forward bias prof j. Semiconductors pn junction theory interview questions and answers pdf free download. In this tutorial, we will learn about pn junction diodes and in particular the characteristics and working of pn junction diode. Group iv semiconductor produces ntype or ptype semiconductors. In this type of diode, we dope one side of a semiconductor piece with an acceptor impurity and another side with a donor impurity.
Junction coming to the equilibrium by balancing the fermi level ef ef the balance is achieved by electrons diffusing into a pside bringing an extra negative charge in there and by the holes diffusing into. Tunnel diode working principle and characteristics ece. Junction coming to the equilibrium by balancing the fermi level ef ef the balance is achieved by electrons diffusing into a pside bringing an extra negative charge in there and by the holes diffusing into an nside bringing an extra negative charge in there pn. Ec8252 electronic devices ed regulation 2017 unit i semiconductor diode. The fermi levels and are displaced relatively by an amount ev equal to the potential energy due to the applied voltage, v which cause the displacement. Electrons diffuse from the emitter into the base and holes diffuse from the base into the emitter. It is a region in which no electron can stay as there is no allowed energy state. In tunnel diode, the valence band and conduction band energy levels in the ntype semiconductor are lower than the valence band and conduction band energy levels in the ptype semiconductor. Basic diode electronics introduction to diodes the pn junction the pn junction is a homojunction between a ptype and an ntype semiconductor. If somebody is able to understand pn junctions well, it becomes quite easy for him to understand all other.
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