Pn Junction Diode Construction And Working Pdf

pn junction diode construction and working pdf

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An avalanche diode is a special type of semiconductor device designed to operate in reverse breakdown region. Avalanche diodes are used as relief valves a type of valve used to control the pressure in a system to protect electrical systems from excess voltages. Avalanche diodes are generally made from silicon or other semiconductor materials.

What is Diode? Construction & Working of PN Junction Diode

Definition : A special type of PN junction diode that operates in reverse biased mode, more specifically in breakdown region is known as Zener Diode. The doping level of the zener diode is somewhat higher than the normal PN junction diode. So that it can give a sharp breakdown voltage.

Zener breakdown was first noticed and explained by American Scientist C. It is majorly used in voltage regulation in order to keep the voltage constant even when the load shows variation. Its symbol is somewhat similar to the symbol of a normal diode. However, a small variation is seen in the symbol of a zener diode which is shown by the bends at the two ends of the vertical line.

Here, N and P substrate are diffused together. The junction region is covered with a layer of silicon dioxide SiO 2. At the same time during construction, the whole assembly is metallised in order to generate anode and cathode connection. The layer of SiO 2 helps to prevent contamination of the junctions. Thus, is used in the construction of zener diode.

The operation of a zener diode is like a normal diode in forward biased mode. That means a large majority current flows through the device when the forward potential is applied to it. However, a zener shows variation from a normal diode in the aspect of its doping concentration. Zener diode is highly doped thus its depletion width is very thin. Due to this, more current flows through a zener diode as compared to a normal junction diode.

It specifically acts in the breakdown region in the reverse biased condition. A zener diode shows two breakdown approach, zener breakdown, and avalanche breakdown. Avalanche breakdown is usually subjected to happen when the applied reverse bias voltage is high.

As we already know that in reverse biased condition, small minority current flows through a normal diode. When a high reverse biased voltage is applied to the device, the minority carriers experience acceleration and moves with high velocity.

During its movement, minority carriers collide with the atoms and generate more number of free electrons. These free electrons further generate some more free electrons. Thus, a high electric current is generated due to this multiplicative action. Hence, we say high potential in reverse bias is required in case of avalanche breakdown.

This high current is responsible for the permanent destruction of a normal diode. But an avalanche diode carefully manufactured to operate in breakdown region withstand the high current flowing through it. This breakdown mechanism is noticed in diodes that are heavily doped. Due to the high concentration of impurities, the width of the depletion width is narrow. With the increase in reverse potential, a strong electric field is generated by the depletion region.

As the reverse potential is supplied to the device and the voltage reaches near to zener voltage. The electrons present in the depletion region utilize that energy and get separated with the parent atom. Thereby generating free electrons. This action generates more free electrons and hence their movement produces electric current through the device. Thus, a small increase in reverse voltage will cause an immediate increase in current through the device. The current flowing through the device shows its maximal increase up to circuit permissible value.

This reverse current will remain constant for a wide range of reverse potential. When a zener diode operates in the breakdown region, it does not burn rapidly. However, the reason for this is some external circuit is required in order to protect the device from the excess current. The figure represents the curve for both silicon and germanium diodes. The forward characteristic of the zener diode is similar to a normal diode which is clearly seen in the figure above.

In reverse biased condition, a small reverse current flows due to minority charge carriers. On increasing the reverse voltage, current increases. A point is reached when the junction gets destroyed and a sharp increase in current is noticed without any noticeable increase in reverse potential. This voltage is known as zener voltage. The current through the device is limited by making use of external resistance.

Zener voltage : It is that reverse bias voltage at the which junction breakdown completely and large current flows through the device at a constant potential. Reverse saturation current : It is the current flowing through the device at reverse biased condition due to the flow of minority charge carriers. Zener impedance : Zener impedance is basically termed as the dynamic resistance of the zener diode. It is defined as the ratio of small change in zener voltage and current.

It is given by. So, we can conclude that a zener diode is definitely a reverse bias device. As it resembles a normal diode in the forward biased region. It is a heavily doped diode, due to which conductivity increases and breakdown is achieved at low voltage. Your email address will not be published. Skip to content. Key terms related to Zener Diode Zener voltage : It is that reverse bias voltage at the which junction breakdown completely and large current flows through the device at a constant potential.

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pn Junction Diode and Its Working Principle

A diode is formed by joining two equivalently doped P-Type and N-Type semiconductor. When they are joined an interesting phenomenon takes place. The P-Type semiconductor has excess holes and is of positive charge. The N-Type semiconductor has excess electrons. Hence the electron diffuses and occupies the holes in the P-Type material. Causing a small region of the N-type near the junction to lose electrons and behave like intrinsic semiconductor material, in the P-type a small region gets filled up by holes and behaves like a intrinsic semiconductor. This thin intrinsic region is called depletion layer, since its depleted of charge see diagram above and hence offers high resistance.

Characteristics and Working of PN Junction Diode

Definition: The tunnel diode is a highly conductive, heavily doped PN-junction diode in which the current induces because of the tunnelling. The tunnelling is the phenomenon of conduction in the semiconductor material in which the charge carrier punches the barrier instead of climbing through it. The tunnel diode is a heavily doped PN-junction diode. The concentration of impurity in the normal PN-junction diode is about 1 part in 10 8.

In general, all the electronic devices need DC power supply but it is impossible to generate DC power so, we need an alternative to get some DC power thus the usage of diodes comes into the picture to convert AC power to DC power. A diode is a tiny electronic component used in almost all the electronic circuits to enable the flow of current in only one direction unidirectional device. We can say that the usage of semiconductor materials to build the electronic components was started with diodes.

A diode is a two-terminal unidirectional power electronics device. The semiconductor diode is the first invention in a family of semiconductor electronics devices. After that many types of diodes are invented. But today also the most commonly used diode is a semiconductor diode. Generally, silicon is used to make a diode.

Zener Diode

Diode | Working Principle | Construction

A P-N Junction Diode is formed by doping one side of a piece of silicon with a P-type dopant Boran and the other side with a N-type dopant phosphorus. Ge can be used instead of Silicon. The P-N junction diode is a two-terminal device. This is the basic construction of the P-N junction diode. It is one of the simplest semiconductor devices as it allows current to flow in only one direction.

A pn junction diode is a two terminal single crystal semiconductor device whose one side is doped with acceptors and other side by donors. Doping with acceptor creates p type semiconductor while doping with donors produces n type. Thus a pn junction is formed in diode. The formation of pn junction in a single crystal due to doping with p type and n type material is shown in figure below. In the above figure, left side of crystal is p type while the right side is n type.

Tunnel Diode Working

Electrical Academia. Definition: A diode is the simplest semiconductor component. It is made of only two pieces from different semiconductor materials. Nonetheless, you may find diodes in almost all electronic circuits. Its function is to let electric current flow in one direction but to prevent flow in the opposite direction.




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