By applying a negative voltage reverse bias results in the free charges being pulled away from the junction resulting in the depletion layer width being. Animation how a p n junction semiconductor works forward. Jan 29, 2019 so, on an application of a forward bias voltage the width of the depletion region i. Semiconductor pn junction diode is the simplest semiconductor device. The term depletion layer means that the layer is depleted of electrons and holes. Both the processes of drift and diffusion occur in the depletion region in opposite directions.
A pn junction is a boundary or interface between two types of semiconductor materials, ptype. The pn junction possesses essential properties for modern electronics. Physics of semiconductor devices pn junction depletion width. This is the basic construction of the pn junction diode. A free powerpoint ppt presentation displayed as a flash slide show on id.
It is most easily described when the junction is in thermal equilibrium or in a steady state. Ppt pn junction diode powerpoint presentation free to. Movement of electrons and holes when forming the junction. At the pn junction the border of the two types, the mobile electrons in the ntype this is due to the excess electron provided by the ndopan. A pn junction is an interface or a boundary between two semiconductor material types, namely the ptype and the ntype, inside a semiconductor. Pn junction diode and characteristics of pn junction diode. An additional electrons from the n region are repelled by the net negative charge of the p region.
The pside electrons and nside holes can wander into the depletion region and. A depletion region is a natural feature of doping a semiconductor ntype and right next to it ptype. The depletion region is also called as depletion zone, depletion layer, space charge region, or space charge layer. Understanding the pn junction university of new south wales. Hence, in absence of potential barrier across the junction in the forward bias condition free electrons enter into the ptype region and holes enter into the ntype region, where they recombine and. The concentration of these donors and acceptors are selected to give the pn junction desired device properties pnjuntiondiode. By manipulating this nonconductive layer, pn junctions are. It is an area where there is lack of majority current carriers. A pn junction diode is formed by doping one side of a piece of silicon with a ptype dopant boran and the other side with a ntype dopant phosphorus. Most semiconductor devices involve regions with two different kinds of doping, so a pn junction is present in all of them.
With forward bias, the depletion region is narrow enough that electrons can. The following figure shows the depletion region of a junction diode. Pdf barrier potential across semiconductor pn junction and. 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. P type and n type semiconductors, takenseparately are of very limited use. Contains a ptype and an ntype region in a closed boundary. Normally, a depletion region is developed when pn junction is formed. In this physics digital electronics video lecture in hindi for class 12 we explained forward and reverse bias in pn junction diode in terms of depletion layer and potential barrier. The same is true of an ndoped semiconductor, but the junction between them can become depleted of charge carriers, and hence nonconductive, depending on the relative voltages of the two semiconductor regions. Any semiconductor junction will contain a depletion region of nonconducting semiconductor between the two conducting regions. A voltage applied between gate and source with a polarity to forward bias the pn junctions will reduce the depletion regions to form conduction channels which allow. It is one of the simplest semiconductor devices as. Understanding the depletion region is key to explaining modern semiconductor electronics.
In other words, why voc of schottky contact is smaller than the pn junction. Pn junction diode baising and its vi characteristics. What are the depletion width in the n region, the depletion width in the p region, and the builtin potential at 300k. By manipulating this nonconductive layer, pn junctions are commonly used. This continues to happen till equilibrium is reached. Depletion layer opposes only the the majority carrier not minority carrier. Similarly, o an additional holes from the p region are repelled by the net positive charge of the n region. Pn junction diode multiple choice questions answers. The diffusion of majority charge carriers have to cross the potential barrier vb of the pn junction formed as the effect of the depletion region. Semiconductor devices depletion zone tutorialspoint. The capacitance related to the charge in the depletion layer is called junction capacitance. Because of the structure of a semiconductor junction, the effective width of this depletion layer is not constant. The spacecharge region is extended mainly to the lowdoped side of the pn. The concentration of these donors and acceptors are selected to give the pn junction desired device properties pn juntiondiode.
Mobile electrons of pside of the pn junction diode constitute. Jul 31, 2017 in this physics digital electronics video lecture in hindi for class 12 we explained forward and reverse bias in pn junction diode in terms of depletion layer and potential barrier. There are a few basic concepts to be introduced, such as energy bands, drift and diffusion currents, etc. Pn junction theory for semiconductor diodes electronicstutorials.
For some time the electrons move back from p to n in the space region or depletion layer and some holes move back from n to p in the space region. By exploring the electrical properties of silicon, it is possible to acquire an understanding of the inner workings of the pn junction. One terminal of pn junction diode is anode and other is cathode. Pn junction tutorial introduction to pn junction diodes. From reverse bias capacitancefrequency measurements, at a reverse bias voltage of. The energy level sketch above right is a way to visualize the equilibrium condition of the pn junction. The barrier increase reduces the majority carrier diffusion to a negligible level. A diode is a simple device, which can be implemented by a pn junction, as well as other hetero junction structures.
Under the influence of a strong reverse electric field within the junction s depletion region, electrons have enough kinetic energy that, when they collide with the atoms of the crystal lattice, additional electronhole pairs are formed figure 12. Avalanche noise is created when a pn junction is operated in the reverse breakdown mode. This shall mean that majority charge carriers of the ntype and ptype should at least attain energy of qvb electron volts ev before it will surmount the barrier and diffuse into either ptype or n. May 19, 2014 for some time the electrons move back from p to n in the space region or depletion layer and some holes move back from n to p in the space region. Pn and metalsemiconductor junctions the gmu ece department. The depletion region acts like a wall between ptype and ntype semiconductor and prevents further flow of free electrons and holes. The figure below shows the condition after the formation of depletion region. Dashed line show the boundaries of the depletion region vbi junction2 1 0 1 2 distance m 00. This recombination of electrons and holes produces a narrow region at junction called depletion layer. Depletion region definition depletion region is a region near the boundary of a pn junction region. The depletion region is so named because it is formed from a conducting region by removal of all free charge carriers, leaving none to carry a current.
The pn junction is the fundamental building block of the electronic age. Semiconductors, diodes, transistors horst wahl, quarknet presentation, june 2001 electrical conductivity. Pdf on dec 31, 2011, toshifumi sugiura and others published barrier. Doped semiconductors ntype materials ptype materials diodes and transistors. Atoms in the depletion region are depleted of majority charge carriers and are ionized. Semiconductor pn junction diode working pn diode vi. The regions near the pn interface lose their neutrality and most of their mobile carriers, forming the space charge region or depletion layer see figure a. These two layers of positive and negative ions form the depletion region. Near the junction, electrons diffuse across to combine with holes, creating a depletion region. Pn junction in equilibrium no bias applied diffusion across the junction causes a lot of electrons and holes to recombine leaving a depletion region in proximity of the junction the fixed ions left behind create an electric field the electric field opposes the diffusion of holes in the n region and free electrons in the p region.
Outline about pn diode pn junction formation pn junction realization barrier height thermal equilibrium equilibrium depletion approximation abrupt junction pn junction bias. Biased pn junction when a positive voltage is appliedon p side, the equilibrium is destroyed and a net current can flow 9 simplifyingassumptions. 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. Diffusion across the junction causes a lot of electrons and holes to recombine leaving a depletion region in. Barrier potential across semiconductor pn junction and resting membrane potential. The effect of adding this additional energy source results in the free electrons being able to cross the depletion region from one side to the other. Figure 42 the rectifying iv characteristics of a pn junction. Explore the pn junction simulation tool in order to understand depletion. Movement of electrons and holes when forming the junction depletion region approximation. The animation below shows the formation of the e at the junction between n and ptype material. Silicon a single silicon atom consists of fourteen negatively. Within the depletion region, there are very few mobile electrons and holes. With the gate electrode left open circuited, the pn junction depletion regions between the gate and the epitaxial layer prevent the conduction of current between source and drain. The term depletion refers to the fact that the region near the junction is depleted of their respective majority charge carriers.
This region is called the depletion region since the electric field quickly sweeps free carriers out, hence the region is depleted of free carriers. The solid circles on the right of the junction represent the available electrons from the ntype dopant. The pside or the positive side of the semiconductor has an excess of holes and the nside or the negative side has an excess of electrons. The depletion region of a pn junction is one that is depleted of. Us63555b1 asymmetric depletion region for normally off.
The result is a region near the junction that acts to repel the mobile charges away from the junction through the electric field that these charged regions create. A depletion region forms instantaneously across a pn junction. Depletion region created across the pn junction by the initial movement of majority carrier across the junction. Since the voltage drop across the channel increases from source to drain, the reverse bias of the pn junction also increases from source to drain. Pn junction diode and diode characteristics electronicstutorials. Investigation of a barrier layer by the thermoprobe method pdf. Since the depletion region is a function of bias, the depletion region also gets wider from source to drain, causing the channel to become tapered as shown in red in the figure. As the depletion layer built up a different of potential appears across the junction this difference of potential at junction is called potential barrier.
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