The Diode | complete course 

What is a diode? What are the uses of a diode ?, What is the method for checking the diode ?, What is the symbol of the diode and what is a light diode? What is the difference between the diode and the transistor? All of these are questions about LEDs that always come to our minds, and they will be answered, God willing, some of them will be on this topic and others will be devoted to separate topics because there is a lot of talk about this electronic component.

Definition of a diode

 A diode is defined as a two-way electronic component that only operates in one direction (as long as it is operated within a specified voltage level). So that an ideal diode has zero resistance in one direction, and infinite resistance in the opposite direction. Although in the real world, the diode cannot achieve zero or infinite resistance. Instead, the diode will have a small resistance in one direction (to allow the electric current to flow), and a very high resistance in the opposite direction (to prevent the flow).

 The diode is similar to a circuit valve. Semiconductors are the most common type of diode. These diodes begin to conduct electricity only if a certain seuil threshold voltage is present in the forward direction (ie, the “low resistance” direction). When contacting inside a circuit in the opposite direction (ie the direction of "high resistance"), the diode is said to be reversible. The diode only blocks the current in the opposite direction (i.e. when it is inverted) while the reverse voltage is within a specified range i.e. a specified electrical effect. Above this range, the reversal septum breaks. The voltage at which this breakdown occurs is called a "reverse breakdown voltage".

When the circuit voltage is higher than the reverse breakdown voltage, the diode is able to conduct electricity in the opposite direction (that is, the "high resistance" direction). That is why in practice we say that a diode has a high resistance in the opposite direction - not an infinite resistance. The name of the diode is derived from "diode" which means two-electrode device.

Diode symbol

Arrowhead points in the direction of flow in case of forward bias. This means that the anode is connected to the positive p side and the cathode is connected to the n side which we consider to be negative. The diode is constructed mostly from crystalline silicon or germanium. The anode is denoted by p while the cathode is denoted by the letter n.

Diode working principle

The principle of operation of a diode is based on the interaction of n-type and p-type semiconductors. N-type semiconductors have many free electrons and very few holes. In other words, we can say that the concentration of free electrons is high and the holes are very low in n-type semiconductors. Free electrons in n-type and p-type semiconductors are referred to as charge carriers, p-type semiconductors have a high concentration of holes and a low concentration of free electrons exactly opposite of n. Holes in p-type semiconductors are majority charge carriers, and free electrons in p-type semiconductors are minority charge carriers.

Imagine with me when the n-region and the p-region communicate. Here due to the difference in concentration, the charge carriers are spread from side to side. Since the focus of the holes is high in the p region and low in the n region, the holes begin to spread from the p region to the n region. Again, the concentration of free electrons is high in the n region and low in the p-region and for this reason, the free electrons begin to diffuse from the n-type region to the p-type region. The free electrons that diffuse in the p region and the n region will combine with the holes available there and create negative ions in the p region. In the same way, the holes that diffuse into the n region of the p region will combine with the free electrons available there and create positive ions in the n region. In this way, a layer of negative ions will appear in the p side and a layer of positive ions in the n region along the ntersection line of these two types of semiconductors.

Now let's imagine the following, if the positive terminal of the source is connected to the p side and the negative terminal of the source is connected to the n side of the diode and if we slowly increase the voltage of this source from zero. Initially, there is no current flowing through the diode. This is because even though an external electric field is applied across the diode but the majority charge carriers still do not get enough effect. Majority charge carriers begin to cross the forward voltage barrier only when the value of externally applied voltage across the junction is more than the forward bulk potential. For silicon diodes, the front barrier potential is 0.7 V and for germanium diodes, it is 0.3 V. When the externally applied forward voltage across the diode becomes more than the forward bulk potential, the majority free charge carriers begin to cross the septum and contribute to the forward diode current.

If the reverse voltage across the diode is increased beyond the safe value, due to higher strength and due to higher kinetic energy of charge vector carriers colliding with atoms, then a number of covalent bonds will be broken into a large number of electrons. The huge number of these generated charge carriers contributes to reversing the tremendous current in the diode. If this current is not constrained by an external resistance connected to the diode circuit, the diode may be permanently destroyed.