Diode

What is a Diode?

A diode is an electronic component that has two terminals and conducts the current in one direction. An ideal diode will have zero resistance in forward biasing and infinite resistance in reverse biasing.

The most common type of diode is a p-n junction. In this type of diode p-type semiconductor material (the majority of charge carriers are holes) and n-type semiconductor material (the majority of charge carriers are electrons) are combined by different types of fabrication techniques and form a p-n junction diode. such a p-n junction is produced by any of the following fabrication techniques:

  1. Epitaxial Grown or Planner Diffused Junction

  2. Fused or Alloy Junction

  3. Diffused Junction

  4. Recrystallized Junction

  5. Point Contact Junction

  6. Surface Barrier Junction


** These fabrication techniques have been discussed in another post

Working Principle of Diode:

A diode’s working principle depends on the doping of n-type and p-type semiconductors. An n-type semiconductor has a large number of free electrons and very few numbers of holes. In other words, we can say that the concentration of free electrons is high and that of holes is very low. Free electrons in the n-type semiconductor are known as majority charge carriers, and holes in the n-type semiconductor are known as minority charge carriers.

Similarly, A p-type semiconductor has a high concentration of holes and a low concentration of free electrons. Holes in the p-type semiconductor are majority charge carriers, and free electrons in the p-type semiconductor are minority charge carriers.

As the p-n junction is created by the fabrication technique, the diffusion process starts at the junction. The majority carrier electron in n-type semiconductor flow toward the p-type semiconductor and the majority carrier holes in p-type semiconductor flow towards the n-type semiconductor and these charge carriers diffused at the junction and form a layer which is called the depletion layer. The potential across the depletion layer is called the potential barrier and this potential creates an internal electric field that opposes the flow of charge carriers. When this internal electric field is sufficiently high then the flow of charge carriers stop. This is called the working of zero biasing diode or unbiased diode.

Biasing of Diode:

When a diode is connected to the external potential energy like a battery, this is known as the biasing of a diode. The connection of external potential energy can be followed by two methods:

1. Forward Biased Diode:

When a p-type semiconductor is connected to the positive terminal(or positive potential) of the battery and the n-type semiconductor is connected to the negative type (negative potential) of the battery then this connection is known as forward biasing.

2. Reverse Biased Diode:

When a p-type semiconductor is connected to the negative terminal (or negative potential) of the battery and the n-type semiconductor is connected to the positive type (positive potential) of the battery then this connection is known as Reverse biasing.

Ideal Diode Equation:

$I_{D}=I_{S}(e^{\frac{qV_{D}}{\eta kT}}-1)$

Where
$I_{D}$ = Diode current
$I_{S}$ = Temperature dependent Saturated Currentq = Charge of an Electrons
$k$ = Boltzmann's Constant which has value $1.381×10^{-23}$
$V_{D}$ = Voltage across the Diode in voltĪ· = An Identity Factor

V-I Characteristic of Diode:

1. Forward Bias:

When a p-type semiconductor is connected to the positive potential and the n-type semiconductor is connected to negative potential so an external electric field is applied across the p-n junction diode. This external electric field, which is applied by a battery, is in the opposite direction of an internal electric field of the diode so the depletion layer decreases as the external electric field increases. Thus current flows from p-type semiconductor to n-type semiconductor. It is due to a reduction in the internal electric field. When the external field is sufficiently high then a very large amount of current is start to flow very rapidly.

2. Reverse Bias:

In reverse biasing, the external electric field (applied electric field) is in the direction of an internal electric field of the diode due to this space region created at the junction and there is no flow of any charge carrier. As the external electric field increases then potential energy also increases so that some of the minority carriers across the junction and very a small amount of the current flows. As the potential energy increases, the kinetic energy of these minority charge carriers increases, and when the potential energy is sufficiently high then the kinetic energy of minority charge the carrier becomes very high and these high energy minority charge carriers cross the junction and collide with a covalent bond. And these minority carrier transfers their energy to covalent bond which causes the rupture of covalent bonds and this causes a very rapid increase in current. This phenomenon is known as Avalanche breakdown.

Applications of Diode:There are the following common applications of the diode:

  1. Rectifier

  2. Clipper Circuits

  3. Clamping Circuits

  4. Reverse Current Protection Circuits

  5. In Logic Gates

  6. Voltage Multipliers

  7. Radio Demodulation

  8. Ionizing Radiation Detectors


A diode has much more applications apart from their common application

Types of Diode:The types of diode include:

  1. Zener diode

  2. P-N junction diode

  3. Tunnel diode

  4. Varactor diode

  5. Schottky diode

  6. Photodiode

  7. PIN diode

  8. Laser diode

  9. Avalanche diode

  10. Light-emitting diode

  11. Thermal Diode

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