Before happening to define the diode and his use in the field of the electronics, it is imprencidible to learn his components. We know to the semiconductors like conductive villains of the electric current, precisely for the difficulty to allow to snatch electrons by virtue of his linkage covalente. But: what happens if we introduce between them impurities in his constitution placing a few strange atoms that have 5 valency electrons, or 3 valency electrons? We can find elements of these characteristics, such as arsenio (Expert), the antimony (Sb), the phosphorus (P), the cueales have 5 valency electrons. And those of 3 electrons, such as the Indian (In), the Gallium (Ga) and the aluminum (To).

Crystal N: Introducing a few arsenio's atoms on the atomic structure of the germanium, which is called doped, the resultant structure stays of the way that arsenio's atom integrates inside the union covalente of the germanium atoms, but the remaining electron now has no capacity in the system, so that it stays like free electron. If now we apply to one and another end of the material, there will be established a route of step of the electrons from the negative pole to the positive, so that the crystal becomes a driver. To this type of crystal he is named a driver N, and to the crystal that forms it crystal N or of type N.

Crystal P: Pondemos to do another conbinación that is going to consist of the introduction of the impurity by means of using a few atoms that have only 3 valency electrons. If we dope the material with Indian, for example, and this one begins to be part of the structure of the crystal, there will be an atom that will have his shared exterior orbit only 7 electrons and it will provoke the instability of the set, but in ves of remaining with one more electron, it stays with some part of the crystal there is a hollow that some electron has to fill. It happens that for the nature of the atoms, the atom that the huecosuele has to remain with the most next electron that his alcanze has left, and that in this case another atom remains without electron and as a consequence of which this situation is carried out at big speed, it might speak about a hollow that is constantly moving for the whole crystal. This way the crystal turns out to be positive (of type P) because if we apply a power supply to him, there will be established a circulation of hollows of the positive pole to the negative, that is to say, the electrons will have found the route of the hollows to cross the whole crystal.

When we join a crystal P with a crystal N, we are created an element of enormous importance in the electronics: the Diode

In effect: let's suppose that we take a germanium piece and dope an end of the same one with Indian, creating a few hollows in the orbits of his exterior electrons. The opposite end of this piece takes drugs with arsenio so that an electrons excess is created, this way the part of crystal is P and the part of crystal N. In the central part the practically pure material is supported, so that there forms an area that the electronic ones call a resistance area and also exhausted area (area Z). Here, in the precincts of the areas P and N the hollows of the germanium P have been occupied by the free electrons of the germanium N, by what does not exist in this part elements charge carriers. The area Z, therefore, offers a high specific resistance, supporting the diode in rest.

Putting to electrical tests we will see his curious answer, as we have used the germanium to do our experiences, can use the silicon, with what our experience would give the same results.
Let's take an electric current source and we apply the negative terminal on the crystal P and the positive terminal on the crystal N. The result will be a hollows concentration towards the negative pole and of free electrons towards the positive pole, with which the area Z will increase even more his resistance up to the point of which, on having stabilized the exterior orbits of the area Z in a wide scale, very bad driver of the current will endure this part like the germanium not doped, that is to say like a body. And so, there has formed a layer of blockade that blocks the way of the current in this sense.
Now we are going to realize the test the other way round. We connect the positive terminal of the source of current to the crystal P, and the negative terminal to the crystal N. Now the current step produces perfectly the resistance area to itself Z becomes very small; the electrons of the crystal N are repelled by the negative potential of the power supply and they cross the area Z occupying the hollows of the crystal P, which transfers continuously electrons to the positive pole. The crossed intensity is now so much as provided with the generator in accordance with the capacity of step of the diode.

These two experiences show us how this small and simple component can be sometimes a good driver of the current and others bad driver, we see that the resistance that offers this union PN depends on the sense of the polarization. Of P to N there is called he to the sense of the current a step sense, and at the opposite disposal (of N to P) blockade sense. Nearby P it names him by plate, and nearby N, the name of cathode.

He keeps on reading on diodes:

Technical characteristics of the Diodes.
Functions of the Diodes.
Classes of Diodes.
Codes of desidnación of Diodes Semiconductors.