The Diode: Definition, Symbol, and Types of Diodes (2023)

Diode:

A diode is a special two-terminal electronic component that allows the development of electrical flow in only one direction, as long as it operates within a certain voltage range. In an ideal diode, it shows no electrical resistance when current flows in the ideal bearing, while at the same time it shows infinite resistance when current tries to flow in the other direction.

Although in reality, diodes cannot meet zero or infinite resistance. All things being equal, a diode will have negligible resistance in one direction (to allow current flow), and extremely high resistance in reverse heading (to prevent current flow). A diode is really like a valve for an electrical circuit.

Semiconductor diodes are the most popular type of diode. These diodes initiate leading power provided a certain threshold voltage is available in the forward bearing (eg “low impedance” heading). A diode is considered “one-way forward” when conducting current in that direction. At the point when connected within a circuit in a converse course (eg a “high impedance” course), the diode is considered a “one-way resistor”.

A diode is said to be “forward biased” when conducting current in this direction. When connected in the reverse direction (ie the “high resistance” direction) within a circuit, the diode is said to be “reverse biased”.

A diode only blocks current in the reverse direction (ie when it is reverse biased) while the reverse voltage is within a certain range. Above this range, the reverse barrier is broken. The voltage is at which this breakdown occurs is called the “reverse breakdown voltage”.

When the circuit voltage is greater than the reverse breakdown voltage, the diode is able to conduct current in the reverse direction (ie, the “high resistance” direction). This is why in practice we say diodes have high resistance in the reverse direction – not infinite resistance.

A PN intersection is the least complex type of semiconductor diode. Under ideal circumstances, this PN intersection acts as a short out when it is forward one-sided, and as an open circuit when it is converse one-sided. The name diode is gotten from “di-tribute” and that implies a gadget that has two cathodes. These Diodes are usually utilized in numerous gadgets projects and are remembered for a significant number of the best Arduino starter packs.

Diode Symbol:

The symbol for a diode is shown below. The arrow indicates the direction of conventional current flow in the forward-biased condition. This means that the anode is connected to the p side and the cathode is connected to the n side.

We can make a simple PN junction diode by doping a pentavalent or donor impurity in one part and a trivalent or acceptor impurity in the other part of the silicon or germanium crystal block.

These doping form the PN junction in the middle of the block. We can also make a PN junction by combining a p-type semiconductor and an n-type semiconductor with a special fabrication technique. The terminal is connected to the P-type is the anode. The terminal is the cathode connected to the N-type side.

The Working Principle of Diode:

The working principle of diode depends on the interaction of n-type and p-type semiconductors. An n-type semiconductor has many free electrons and very few holes. In other words, we can say that in n-type semiconductor, the concentration of free electrons is very high and the amount of holes is very low.

Free electrons in n-type semiconductor are called majority charge carriers, and holes in n-type semiconductor are called minority charge carriers.

The A p-type semiconductor has a high concentration of holes and a low concentration of free electrons. Openings are the major charge transporters in a p-type semiconductor, and free electrons are the minority charge transporters in a p-type semiconductor.

The Unbiased Diode:

Now we see what happens when an n-type region and a p-type region come together. Because of the concentration difference here, the majority carriers diffuse from one side to the other. Since the concentration of holes is high in the p-type region and low in the n-type region, the holes start spreading from the p-type region to the n-type region.

Again the concentration of free electrons is higher in n-type region and less in p-type region and hence free electrons start to diffuse from n-type region to p-type region.

The free electrons diffusing from the n-type region to the p-type region will recombine with the holes available there and create negative ions exposed in the p-type region. Similarly, holes propagating from the p-type region to the n-type region will recombine with the free electrons available there and produce exposed positive ions in the n-type region.

Thus, a layer of negative ions on the p-type side and a layer of positive ions on the n-type region will appear along the junction line of these two types of semiconductors. The layer of exposed positive ions and exposed negative ions forms a region in the middle of the diode where no charge carriers exist because all the charge carriers recombine here in this region. Due to the lack of charge carriers, this region is called the depletion region.

After the depletion region is formed, there is no further diffusion of charge carriers from one side to the other in the diode. This is because an electric field appears across the region which will prevent the transfer of charge carriers from one side to the other.

The capability of the layer of uncovered positive particles in the n-type side would revoke the openings in the p-type side and the capability of the layer of uncovered negative particles in the p-type side would cancel the free electrons in the n-type side. That implies a potential boundary is made across the intersection to forestall further dissemination of charge transporters.

Forward Biased Diode:

Now let us see what happens if the positive terminal of a source is connected to the p-type side and the negative terminal of the source is connected to the n-type side of the diode and if we gradually increase the voltage of this source. zero

Initially, no current is flowing through the diode. This is because even though an external electric field is applied to the diode, most of the charge carriers still do not get enough influence of the external field to cross the depletion region. As we mentioned the depletion region acts as a potential barrier against the majority charge carriers.

This potential barrier is called the forward potential barrier. Most charge carriers begin to cross the forward potential barrier only when the value of the externally applied voltage across the junction is greater than the forward barrier potential. For silicon diodes, the forward barrier potential is 0.7 volts and for germanium diodes, it is 0.3 volts.

When the externally applied forward voltage across the diode exceeds the forward barrier potential, free-matter charge carriers begin to cross the barrier and contribute to the forward diode current. In this situation, the diode will behave as a short-circuited path, and the forward current is limited only by the resistors connected externally to the diode.

Reverse Biased Diode:

Now we see what happens if we connect the negative terminal of the voltage source to the p-type side and the positive terminal of the voltage source to the n-type side of the diode. In this case, due to the electrostatic attraction of the negative potential of the source, the holes in the p-type region will migrate farther away from the junction, leaving more exposed negative ions at the junction.

Similarly, free electrons in the n-type region will move farther away from the junction toward the positive terminal of the voltage source, leaving more exposed positive ions in the junction.

As a result of this trend, the degradation region becomes wider. This condition of diode is called reverse biased condition. In this case, none of the majority carriers cross the junction, and they move away from the junction instead. Thus, a diode prevents current flow when it is reverse biased.

As we already mentioned at the beginning of this article p-type semiconductor always has some free electrons and n-type semiconductor always has some holes. In a semiconductor these opposite charge carriers are called minority charge carriers.

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