¿Qué es un semiconductor? - una explicación sencilla.

Electronics in less than a century has advanced so rapidly thanks to the fact that we found some elements that we call semiconductors. With them we have found the perfect combination of an insulator and a conductor. For that reason, several electronic devices in the world exist and work.

The conductors and insulators separately are of great importance, since an electric conductor is that material that offers little resistance to the flow of charges, and on the other hand, the insulators are the opposite of a conductor, these resist the passage of electrical charges and retain them. How does a semiconductor achieve this?

By the time of this video, there are these 14 elements, being silicon and germanium the most popular, but in particular we use silicon a lot.

Most of the electronic devices we have contain chips of this material, since it is a very abundant material that we can easily find in the sand, and after an industrial process we can obtain pure silicon. The special thing about these elements is the amount of electrons they contain in their last orbit. As several of them share the same group in the periodic table, we can know how many electrons are in their last orbit.

For example, cadmium will have 2, aluminum will have 3, silicon will have 4, phosphorus 5, and selenium 6. What is the point of knowing this? These elements, by themselves, are not so special. To be able to use them, we have to form pairs, and depending on what pairs we form, these can be used to do many interesting things like LEDs, thermistors, transistors, and diodes, among many other things.

Let's take silicon as an example, since it is the most used today. It has 4 electrons in its last orbit. If we grab many silicons and put them together in a net shape, they fulfill the octet rule, which says that atoms tend to complete their last levels of energy with a quantity of 8 electrons, to achieve stability, and form a link that we call covalent, which means that they share electrons in their last level. Chemically, this is the perfection.

Now, if we put a battery in this stable silicon network and induce a flow of electrons, nothing will happen, since the electrons in the battery will not be able to move through the network because the electrons in it are very close together, so there is no need to wander around there. In this case, silicon behaves like an insulator.

For silicon to stop acting as an insulator and behave like a conductor, we have to introduce impurities to the material. There are two ways to do this, one of them is by introducing electrons and the other by introducing holes. This process of adding impurities is known as doping and we can only do it with other semiconductors.

Returning to the silicon network, if we doped the network with phosphorus, which has 5 electrons, the network will now have links of silicon-phosphorus and the octet rule is fulfilled. But now for each union we have a free electron and these electrons will be floating through the network. Now, if we put a battery, the floating electrons will be attracted by the positive side of the battery and the flow of electrons will begin. In this example we have doped our network with electrons.

But if we adopt the silicon network with a material like boron, which has three electrons, we will obtain unions of silicon-boron. And now the octet rule is not fulfilled, because where we would have an electron, now we have a hole. With this we refer to the absence of an electron.

So what happens is that the electrons in the network will be moving constantly to cover that hole. But even if the electrons are accommodated, there will always be a hole. So it will seem that the hole is the one that moves. But it's not really like that, because the only thing that moves is the electron. Now, what happens if we put a battery to this network?

Well, the electrons will continue to be attracted by the positive side and in turn the electrons on the negative side will want to cover the holes, so this movement will make the flow of charges possible. In this example we have doped our network with holes. When we do not doped our network with any impurity, it is known as an intrinsic semiconductor, which is a pure semiconductor and at ambient temperature behaves like an insulator.

This also means that the number of holes and electrons is the same. When we dope our network with electrons, it is known as an extrinsic semiconductor type N. And when we dope it with holes, it is called an extrinsic semiconductor type P. The combination of semiconductors type N and P has given us the components of electronics with which we have been able to achieve the whole modern world in which we live today.

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