Any semiconductor junction will contain a depletion region of nonconducting semiconductor between the two conducting regions. In other words, why voc of schottky contact is smaller than the pn junction. 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. Depletion region definition depletion region is a region near the boundary of a pn junction region. P type and n type semiconductors, takenseparately are of very limited use.
Most semiconductor devices involve regions with two different kinds of doping, so a pn junction is present in all of them. Figure 42 the rectifying iv characteristics of 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. This region is called the depletion region since the electric field quickly sweeps free carriers out, hence the region is depleted of free carriers. Pn junction tutorial introduction to pn junction diodes. One terminal of pn junction diode is anode and other is cathode. By manipulating this nonconductive layer, pn junctions are. Us63555b1 asymmetric depletion region for normally off.
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. 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. The following figure shows the depletion region of a junction diode. Semiconductor devices depletion zone tutorialspoint. A pn junction is an interface or a boundary between two semiconductor material types, namely the ptype and the ntype, inside a semiconductor. There are a few basic concepts to be introduced, such as energy bands, drift and diffusion currents, etc. If the depletion layer region has a distance d, it therefore must therefore penetrate into the silicon by a distance of dp for the positive side, and a distance of dn for. Barrier potential across semiconductor pn junction and resting membrane potential. Explore the pn junction simulation tool in order to understand depletion. Dashed line show the boundaries of the depletion region vbi junction2 1 0 1 2 distance m 00. Shockley model from sze, 1981 vv at 1 j j e tot s n n p p p n s l d n q l d p j. An additional electrons from the n region are repelled by the net negative charge of the p region.
The pn junction is the fundamental building block of the electronic age. A pn junction is a boundary or interface between two types of semiconductor materials, ptype. A depletion region is a natural feature of doping a semiconductor ntype and right next to it ptype. 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. 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 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. Silicon a single silicon atom consists of fourteen negatively. Atoms in the depletion region are depleted of majority charge carriers and are ionized. As the depletion layer built up a different of potential appears across the junction this difference of potential at junction is called potential barrier. These two layers of positive and negative ions form the depletion region.
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. With forward bias, the depletion region is narrow enough that electrons can. Semiconductors, diodes, transistors horst wahl, quarknet presentation, june 2001 electrical conductivity. The animation below shows the formation of the e at the junction between n and ptype material. A free powerpoint ppt presentation displayed as a flash slide show on id. Pdf on dec 31, 2011, toshifumi sugiura and others published barrier.
Mobile electrons of pside of the pn junction diode constitute. The barrier increase reduces the majority carrier diffusion to a negligible level. The pn junction possesses essential properties for modern electronics. When the bias va applied to the junction is varied, the width of the depletion region changes according to. This continues to happen till equilibrium is reached. 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. 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 depletion region of a pn junction is one that is depleted of. Physics of semiconductor devices pn junction depletion width. A diode is a simple device, which can be implemented by a pn junction, as well as other hetero junction structures. The depletion region acts like a wall between ptype and ntype semiconductor and prevents further flow of free 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. Diffusion across the junction causes a lot of electrons and holes to recombine leaving a depletion region in.
The pside electrons and nside holes can wander into the depletion region and. Similarly, o an additional holes from the p region are repelled by the net positive charge of the n region. Animation how a p n junction semiconductor works forward. Physics of semiconductor devices pn junction depletion width problem a silicon pn diode has a doping of n d 81015 1 cm3 and n a 210 16 1 cm3. 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. The spacecharge region is extended mainly to the lowdoped side of the pn. Doped semiconductors ntype materials ptype materials diodes and transistors. Jan 29, 2019 so, on an application of a forward bias voltage the width of the depletion region i. Pn junction diode multiple choice questions answers. Semiconductor pn junction diode working pn diode vi. Movement of electrons and holes when forming the junction depletion region approximation. Understanding the pn junction university of new south wales. Movement of electrons and holes when forming the junction.
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. The figure below shows the condition after the formation of depletion region. Ppt pn junction diode powerpoint presentation free to. The concentration of these donors and acceptors are selected to give the pn junction desired device properties pn juntiondiode. Pn junction theory for semiconductor diodes electronicstutorials. Pn junction diode and characteristics of pn junction diode. Understanding the depletion region is key to explaining modern semiconductor electronics. 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. The depletion region is also called as depletion zone, depletion layer, space charge region, or space charge layer. 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. 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. The area where these holes and electrons become depleted is generally known by the term depletion region. 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. Pdf barrier potential across semiconductor pn junction and.
It is most easily described when the junction is in thermal equilibrium or in a steady state. 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. Pn junction diode baising and its vi characteristics. Pn junction diode and diode characteristics electronicstutorials. By manipulating this nonconductive layer, pn junctions are commonly used. The concentration of these donors and acceptors are selected to give the pn junction desired device properties pnjuntiondiode. This recombination of electrons and holes produces a narrow region at junction called depletion layer. Pn and metalsemiconductor junctions the gmu ece department. What are the depletion width in the n region, the depletion width in the p region, and the builtin potential at 300k. It is an area where there is lack of majority current carriers. 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. Near the junction, electrons diffuse across to combine with holes, creating a depletion region. This is the basic construction of the pn junction diode. A depletion region forms instantaneously across a pn junction.
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. Within the depletion region, there are very few mobile electrons and holes. Avalanche noise is created when a pn junction is operated in the reverse breakdown mode. Outline about pn diode pn junction formation pn junction realization barrier height thermal equilibrium equilibrium depletion approximation abrupt junction pn junction bias. 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. Contains a ptype and an ntype region in a closed boundary. Because of the structure of a semiconductor junction, the effective width of this depletion layer is not constant.
Biased pn junction when a positive voltage is appliedon p side, the equilibrium is destroyed and a net current can flow 9 simplifyingassumptions. 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. Depletion region created across the pn junction by the initial movement of majority carrier across the junction. Depletion layer opposes only the the majority carrier not minority carrier. 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. 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 pn junction diode is the simplest semiconductor device. A builtin potential v bi is formed at the junction due to e. The energy level sketch above right is a way to visualize the equilibrium condition of the pn junction. The solid circles on the right of the junction represent the available electrons from the ntype dopant.
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