What happens when we join ptype and ntype semiconductors. It does not correspond to any physical spatial bending. The field at the schottky junction sweeps the electrons into the metal collector just as in the pn basecollector junction shown in fig. Pn junction diode baising and its vi characteristics. Electronic devices ed ee8252 notes pdf free download. The energy band diagram for each cube is displayed directly below it. We have also learned about diffusion current, depletion region. The other affect on the current density through a device is due to the diffusion of free carriers in the device if a special variation of carrier energies or densities exist. In this type of diode, we dope one side of a semiconductor piece with an acceptor impurity and another side with a donor impurity. Dec 27, 2017 this video provides knowledge on how to draw the energy band diagran for a pn junction.
By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction. Here you may find a good video with animation, which explains the formation of pn junction. Energy band diagram of bjt george mason university. A diode is a simple device, which can be implemented by a pn junction, as well as other hetero junction structures. In this video, i go over the band diagram of the pn junction, which will allow us to find the electric field and the pn junction width through what is called the builtin potential vbi. Analogue electronicspn junctions wikibooks, open books for. Hi, i know there are a lot of question similar to this, but i really cant figure out the answer to mine myself. They readily combine with those holes, making possible a continuous forward current through the junction.
Module 2 essentially, they serve the same function in circuits, as the valves in your heart and. 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. 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. Lecture 16 the pn junction diode ii free online course. 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. Diodes are electronic check valves which allow current to flow freely in one direction, but block current flow in the opposite direction. Draw the energy band diagram of pn junction diode in. Module 1 semiconductor pnjunction diodes what are they and what is their purpose. If the junction is highly doped then the depletion region can be very thin. Draw to scale the energy band diagram of the junction at equilibrium. The energy diagram of the basecollector junction would be similar to fig.
Recall that these particles will have kinetic energy due to heat. Pn junction diode and characteristics of pn junction diode. In silicon, the bonding energy of the covalent bond is 1. 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. The upward direction in the diagram represents increasing electron energy. In this lecture, i discussed about the energy band diagram of the pn junction in equilibrium.
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. Impurities donors andor acceptors can be added to each side, and the resulting change in the energy band diagram can be observed directly below each cube. Oct 05, 2017 in this lecture, i discussed about the energy band diagram of the pn junction in equilibrium. Review, pn junctions, fermi levels, forward bias prof j. When ptype material meets ntype material within a single silicon crystal a pn junction is formed. Pn junction tutorial introduction to pn junction diodes. When a bond is supplied with this amount of energy or more an elec tron can break free. Sir the graph have you have shown does it have an end point. The pn junction is the fundamental building block of the electronic age. Smith department of eecs university of california, berkeley eecs 105 spring 2004, lecture 19 prof. Barrier potential across semiconductor pn junction and resting membrane potential.
Unit i semiconductor diode ec8252 electronic devices notes. Electrons and holes reach an equilibrium at the junction and form a depletion region. Ev ec thin junction heavily doped 2 0 v vbi r w qn. Pn and metalsemiconductor junctions higher education. A pn junction band diagram when the two semiconductors are in contact. 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. The energy band diagram of an ideal ptype substrate mos capacitor at zero bias is shown in figure 3.
The student then brings the material together and can create a number of pn junction devices. When a pn junction is forward biased then its energy band diagram looks like this. Jul 06, 2016 the free electrons in the n region that occupy the upper part of the conduction band in terms of their energy can easily diffuse across the junction they do not have to gain additional energy and temporarily become free electrons in the lower part of the pregion conduction band. If this energy is sufficiently large, a particle can still diffuse. At high reverse bias, the conduction and valence bands on the opposite sides of the junction are very close to each other. This transfer of electrons and holes back and forth across the pn junction is. Energy band diagram of a pn junction a before and b after merging the ntype and ptype regions. The free electrons in the n region that occupy the upper part of the conduction band in terms of their energy can easily diffuse across the junction they do not have to gain additional energy and temporarily become free electrons in the lower part of the pregion conduction band.
The effect of adding this additional energy source results in the free electrons being able. Pn junction forward bias condition is used in all led lighting applications. 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. Apr 05, 2019 pn junction is formed in a single crystal by joining two ntype and ptype semiconductors. In an ideal mos capacitor, the metal work function. The term band gap refers to the energy difference between the top of the valence outer electron band and the bottom of the conduction free electron flow band. E equilibrium currents for pn junction in equilibrium there are still small currents flowing across. Pn junction diode in the reversebiased configuration is sensitive to light from a range between 400nm to nm, which includes visible light.
For a pn junction at equilibrium, the fermi levels match on the two sides of the junctions. Pn junction diode and diode characteristics electronics tutorials. This charge transfer of electrons and holes across the pn junction is known as diffusion. Chapter 5 spring 2003 ee lecture 10, slide 2 ntype ptype. A pn junction diode is a twoterminal electronics element, which can be classified as either step graded or linear graded. Consider the the band diagram for a homojunction, formed when two bits of the same type of semiconductor e.
It will help you to grasp concepts behind pn junction even better. Sep 24, 2005 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. Cu, ag, au partially filled band full band empty band. Energy diagram for pn junction the potential energy difference between the two sides of the junction is given by electric field in the depletion region. The pn junction is of great importance as it is the main control element for the semiconductor devices. The region around m contains the space charge layer scl. Electrons in the two bits have different electrochemical potentials i. Electronics tutorial about the pn junction diode and the vi characteristics of pn. Most semiconductor devices involve regions with two different kinds of doping, so a pn junction is present in all of them. Jan 29, 2019 pn junction diode is one of the fundamental elements in electronics. We can then fill in the junction region of the band diagram as. P type and n type semiconductors, takenseparately are of very limited use.
Contacts are made to all three regions, the two outer regions called the emitter and collector and the middle region called the base. Here we have p and n material and this area right here is the area were referring to as the pn junction. 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. 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. The fermi level lies close to the conduction band in ntype material and it is close to valence band in ptype material. Also, note that this flatband diagram is not an equilibrium diagram since both electrons and holes can lower their energy by crossing the junction. 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. Energy band diagram an overview sciencedirect topics. On the nside of m, scl has the exposed positively charged donors, whereas on the pside it has the exposed negatively charged. 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. Questions you should be able to answer by the end of todays lecture. Energy band diagram spring 2003 ee lecture 10, slide 6. There are a few basic concepts to be introduced, such as energy bands, drift and diffusion currents, etc. 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.
When a pn diode is made with ptype and ntype materials, then flow of free charge carriers takes place at the junction. 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. When two dissimilar materials are joined, there is an offset in the energy levels. It would be effective collecting the electrons arriving at this junction from the p type base to the metal.
Heat, light, and other stimuli can excite electrons across the band gap, resulting in. 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. When a ptype semiconductor is joined to an ntype semiconductor, the interface between the two is called a pn junction because the electron concentration in the ntype material is much higher than in the ptype material, electrons will tend to diffuse across the junction into the ptype material. The term pn junction refers to the joint interface and the immediate surrounding area of the two semiconductors. Draw the energy band diagram of pn junction diode in forward and reverse bias condition. Semiconductor junctions semiconductor technology video lecture. When looking at a band diagram, the electron energy states bands in a material can curve up or down near a junction. I have developed a second chapter on the series, which explains the characteristics of pn junction diode. Most semiconductor devices contains one or more pn junctions. Find the builtin voltage, and compare with the value measured off.
Electronics tutorial describing the semiconductor pn junction and pn. Silicon a single silicon atom consists of fourteen negatively. A pn junction is a boundary or interface between two types of semiconductor materials, ptype and ntype, inside a single crystal of semiconductor. After crossing the junction, the electrons quickly lose energy. 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. Pdf barrier potential across semiconductor pn junction and. A bipolar junction transistor consists of two backtoback pn junctions, who share a thin common region with width, w b. Step pn junction energy band diagram physics forums. An extra electron jumps into the conduction band and gets free.
402 1509 702 1365 591 887 1616 270 1310 202 1596 1603 511 1227 372 1296 54 1632 1550 4 936 529 343 534 924 187 582 279 248 633 1391 216