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:
- Epitaxial Grown or Planner Diffused Junction
- Fused or Alloy Junction
- Diffused Junction
- Recrystallized Junction
- Point Contact Junction
- 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 voltη = 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:
- Rectifier
- Clipper Circuits
- Clamping Circuits
- Reverse Current Protection Circuits
- In Logic Gates
- Voltage Multipliers
- Radio Demodulation
- Ionizing Radiation Detectors
A diode has much more applications apart from their common application
Types of Diode:The types of diode include:
- Zener diode
- P-N junction diode
- Tunnel diode
- Varactor diode
- Schottky diode
- Photodiode
- PIN diode
- Laser diode
- Avalanche diode
- Light-emitting diode
- Thermal Diode
