What is p n junction in electronics

By Zukasa | 23.02.2021

what is p n junction in electronics

p n Junction

P-n junction, in electronics, the interface within diodes, transistors, and other semiconductor devices between two different types of materials called p -type and n -type semiconductors. These materials are formed by the deliberate addition of impurities to pure semiconductor materials, such as silicon. Semiconductors of p -type contain holes, mobile vacancies in the electronic structure that . A p-n junction is an interface between p-type and n-type semiconductor materials within a single semiconductor crystal. One side of the junction is a p-type doped semiconductor, and the other side is an n-type doped semiconductor.

Lesson 0 : Module 2 Introduction. Lesson 1 : Electric Circuits. Lesson 2 : Electric Power Sources. Lesson 3 : Electric Current. Lesson 4 : Voltage. Lesson 5 : Electrical Resistance. Lesson 7 : Electric Power. What time does the london marathon start 0 : Introduction to Module 3.

Lesson 1 : Introduction to DC Circuits. Lesson 2 : Series and Parallel Circuits. Lesson 4 : Resistors, Capacitors, and Inductors. Lesson 5: Resistors in Series. Lesson 6: Resistors whah Parallel. Lesson 7: Voltage Dividers. Lesson Capacitors. Lesson Dielectric Materials. Lesson Capacitors in Parallel. Lesson Capacitors in Series. Lesson Capacitors in Series and Parallel. Lesson 0 : Module 4 Introduction. Lesson 1 : Alternating Current.

Lesson 2 : AC Juction. Lesson 3 : Impedance. Lesson 4 : Capacitors in AC Circuits. Lesson 5 : Inductors in AC Circuits. Lesson 6 : Transformers. Lesson 0 : Module 5 Introduction. Lesson 1 : Introduction to Semiconductors.

Lesson 2 : Semiconductor Doping. Lesson 3 : P-N Junctions. Lesson 4 : Diodes. Lesson 5: Light Emitting Diodes. Lesson how to find system hardware info : Zener Diodes. Lesson 7 : Transistors. Lesson 8 : Bipolar Junction Transistors. Lesson 0 : Introduction to Analog Circuits.

Lesson 1 : Half-Wave Rectifier. Lesson 2 : Full-Wave Rectifier. Lesson 3 : Bridge Rectifier. A p-n junction is an interface between p-type and n-type semiconductor materials within a single semiconductor crystal. One side of the junction is a p-type doped semiconductor, and the other side is an n-type doped semiconductor. We learned in the last lesson that p-type juncgion n-type semiconductors have distinct electrical characteristicsand that these characteristics electronice be understood by using a band diagram.

When p and n-type semiconductors are combined into a single unit called a iin junctiona new device is created that harnesses the juntcion of both types of material. Just as importantly, p-n junctions form a critical, fundamental building block of almost all semiconductor-based devices including transistors like the m etal o xide s ilicon f ield e ffect t ransistor MOSFET - the foundation of computer processors.

Transistors can even be tested this way, by testing each side of the transistor by pretending that it is simply two separate P-N junction diodes.

P-N junctions are what you get when you combine a p-type semiconductor and an n-type semiconductor, back to back, in a single crystal, with no boundaries between them. It might seem simple, but some surprising things happen as a result. The p-side contains a plethora of free holes and the n-side contains free what were the causes of the spanish- american war. Both sides are electrically neutralas the charged atoms ions on either side balance inn the charge of the free electrons and holes.

On the p-side of the junction, negatively charged ions balance the charge of the free positively charged holes. On the n-side, positively charged ions balance the charge of the free negatively charged electrons. Some interesting things occur before we even place a voltage across the P-N junction. Almost immediately, the situation changes so that we no longer have a simple p-doped section next to an n-doped section.

Since the p-side has free holes that are positively charged and the n-side has free electrons that are negatively charged, there is an attraction between the holes on the p-side and electrons on the n-side. When the electrons and holes meet in the middle, a phenomenon called carrier recombination takes place. The free electrons and holes that meet in the center combine with a release of energy what is p n junction in electronics is how LEDs produce light.

This process happens almost instantaneously, right after the P-N junction is made on the assembly line. The result is that whst p-n junction features two areas that are now electrically charged.

These two areas are eelectronics called the depletion region because there are no free charge carriers left within the region. The right edge of the p-side is the negatively charged area of the depletion region. It has negatively charged ions i.

Without the free holes to keep it neutral, there is a negative charge in this area. Similarly, the left edge eldctronics the p-side now has positively charged ions because the atoms in the N-side of the depletion region have lost their electrons.

The two sides and depletion region in the middle dictate how the p-n junction will behave when we place a voltage across it. A direct current flows from the positive terminal through the circuit to the negative terminal. There are therefore two ways that we can connect a p-n junction to the circuit. We can connect the p-side to the positive terminal and n-side to the negative terminal, which is called forward bias. Or we can shat the p-side to the negative terminal and eleftronics n-side to the positive terminal, which is called reverse bias.

You may have heard that diodes only allow current to pass in one direction, which is jujction rectification. Forward bias is achieved when a p-n junction is placed with the positive terminal of the power source on the p-side and negative terminal on the n-side. Junctiln this juncgion, current flows from the positive terminal as it does in any other circuit.

When the current reaches the p-side, it pushes the holes right toward the middle of the junction. This is because the positively charged holes are repelled by the positive charge at the positive terminal of the power source. At the same time, electrons flow out of the negative terminal of the power source through the side of the circuit leading to the n-side whah the p-n junction.

When these electrons reach the n-side of the p-n junction, they repel the free electrons in the n-side material. The electrons are pushed left toward the center of the junction. Another way of looking at this is that the electrons are attracted to the left by the current. As the holes on the p-side are pushed rightward toward the center and the electrons on the n-side are jnction leftward toward the center, they begin to recombine. This recombination action is how current works in a forward biased p-n junction.

Within the p-n junction, holes j electrons recombine. However, the rest of the circuit is not whqt by the recombination within the junction. The rest junctlon the electdonics functions as normal. The free electron is in the conduction band, and the free hole is in the valence band. Recall that j conduction band is at a higher energy than the valence band; in other words, the electron has more energy than the hole it combines with.

When the electron combines with the hole, what happens is that the high energy electron falls down to elrctronics energy level of the hole. That energy has to go somewhere, so it is released by the electron in the form of a photon, which is a particle of electromagnetic radiation, how to stretch the latissimus dorsi the form of heat or light.

How to calculate the debt ratio, the action does not stop there! As holes move to the right, toward the center of the P-N junction, ix is really happening is that electrons are jumping into eldctronics hole states. In other words, a hole moving to the right whatt with an electron moving to the left. The electron may no longer be in the conduction band, but it can still move via the movement of holes through the p-side, and into the what is a lawn mower carburetor of the circuit.

This is because the valence band of the conductor is above the conduction band. In contrast, a p-n junction that is reverse biased cannot pass current. When a p-n junction is placed in the reverse bias configuration, the junction functions to stop the passage of current. Instead of being pushed toward the center of the junction and recombining, the charge carriers electrons and holes migrate to the edge of each material and prevent current from passing through the junction.

Wht the p-side, the free holes are now attracted to the negative charge supplied by the negative terminal of the power source. Thus the holes migrate what is p n junction in electronics the left, away from the center of the junction. On the n-side, the free electrons are attracted to the positive terminal of the power source. The electrons migrate to what does the new iphone do right, away from the junction.

The junction itself is now relatively free of free charges; with no capability of producing new electrons or juncrion, it becomes insulative and prevents current from continuing to flow.

How P-N Junctions Work

Definition: A p-n junction is an interface or a boundary between two semiconductor material types, namely the p-type and the n-type, inside a semiconductor. The p-side or the positive side of the semiconductor has an excess of holes and the n-side or the negative side has an excess of electrons. In a semiconductor, the p-n junction is created by the method of doping. Apr 24,  · P-N junction Diode is a semiconductor device which has two terminal or two electrodes and allow electric current to flow only in one direction. If diode is in forward biased then it allow current to flow and act as an closed circuit,but if the diode is in reverse biased then it block current flow and act as an open circuit. p n Junction When a p-type semiconductor is suitably joined to an n-type semiconductor, the contact surface so formed is called p-n Junction. All the semiconductor devices contain one or more p n junction. The p-n junction is in effect, the control element for semiconductor devices.

When a p-type semiconductor is suitably joined to an n-type semiconductor, the contact surface is called pn junction. Most semiconductor devices contains one or more pn junctions. The pn junction is of great importance as it is the main control element for the semiconductor devices. In actual practice, a pn junction will not be formed if a p-type block is just brought in contact with n-type block. In fact, pn junction is fabricated by special techniques.

In this method, a small block of indium trivalent impurity is placed on an n-type germanium slab as shown in fig. The system is then heated to a temperature of about o C. The indium and some of the germanium melt to form a small puddle of molten germanium-indium mixture as shown in fig. Under proper conditions, the atoms of indium impurity will be suitably adjusted in the germanium slab to form a single crystal.

The addition of indium overcomes the excess of electrons in the n-type germanium to such an extent that it creates a p-type region. As the process goes on, the remaining molten mixture becomes increasingly rich in indium. When all the germanium has been redeposited, the remaining material appears as indium button which is frozen on the outer surface of the crystallised portion as shown in fig.

At the instant of pn-junction formation, the free electrons near the junction in the n region begin to diffuse across the the junction into the p region where they combine with holes near the junction. As a result n region loses free electrons and this creates a layer of positive charges pentavalent ions near the junction. As the electrons move across the junction, the p region loses holes as the electrons and holes combine. The result is that there is a layer of negative charges trivalent ions near the junction.

These two layer of positive and negative charges form the depletion region or depletion layer. The term depletion is due to the fact that near the junction, the region is depleted i. The depletion layer is formed very quickly and is very thin as compared to the n region and the p region.

Once pn junction is formed and depletion layer is created, the diffusion of free electrons stops. In other words, the depletion layer acts as a barrier to the further movement of free electrons across the junction. The positive and negative charges set up an electric field which acts as a barrier to the free electrons in the n region. This is shown in fig.

There exist a potential difference across the depletion layer known as barrier potential V 0. In electronics, the term bias refers to the use of d. When external d. To apply forward bias, the positive terminal of the battery is connected to p-type and negative terminal is connected to n-type of the pn-junction as shown in fig.

The applied forward potential establishes an electric field which acts against the field due to potential barrier.

Therefore, the resultant field is weakened and the barrier height is reduced at the junction as shown in fig. As potential barrier voltage is very small 0. Once the barrier is eliminated by the forward voltage, junction resistance becomes almost zero and a low resistance path is established for the entire circuit.

Therefore, current flows in the circuit. This is called forward current. When the external d. To apply reverse bias, the positive terminal of the battery is connected to n-type and negative terminal to p-type of the pn junction as shown in fig. The applied reverse voltage establishes an electric field which acts in the same direction as the field due to potential barrier. Therefore, the resultant field at the junction is strengthened and the barrier height is increased as shown in fig.

The increased potential barrier prevents the flow of charge carriers across the junction. Thus, a high resistance path is established for the entire circuit and hence the current does not flow.

Under the influence of forward voltage, the free electrons in n-type move towards the junction, leaving behind positively charged atoms. However, more electrons arrive from the negative terminal of the battery and enter the n-region to take up their places.

As the free electrons reach the junction, they become valence electron. As valence electron, they move through the holes in the p-region. The valence electron move towards left in the p-region which is equivalent to holes moving to right. When the valence electron reach the left end of the crystal, they flow into the positive terminal of the battery.

Volt-Ampere or V-I characteristics of a pn junction is the curve between voltage across the junction and the circuit current. The characteristics can be explained under three conditions namely zero external voltage, forward bias and reverse bias. When the external voltage is zero, i. Therefore, circuit current is zero as indicated by point O in fig. With forward bias to the pn junction i. At some forward voltage 0.

From now onwards, the current increases with the increase in forward voltage. Thus a rising curve OB is obtained with forward bias as shown in fig. From the forward characteristics, it is seen that at first i. It is bacause the external applied volateg is used to overcome the potential barrier. However, once the external applied voltage exceeds the potential barrier voltage, the pn junction behaves like an ordinary conductor. Therefore, current rises very sharply with increase in voltage region AB.

The curve is almost linear. With reverse bias to the pn junction i. Therefore, the junction resistance becomes very high and practically no current flows through the circuit. This is called reverse saturation current I s and is due to the minority carriers. To the free electrons in p-type and holes in n-type, the applied reverse bias appears as forward bias.

Therefore, a small current flows in the reverse direction. If the reverse voltage is increased continuously, the kinetic energy of minority carriers may become high enough to knock out electrons from the semiconductor atom. At this stage breakdown of the junction occurs. This is characterised by a sudden rise of reverse current and a sudden fall of the resistance of barrier region. This may destroy the junction permanently. I am Sasmita. At ElectronicsPost. And, if you really want to know more about me, please visit my "About" Page.

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