Introduction to Electronics - Semiconductors

Semiconductors are the basis of modern electronics. Their applications range from simple components such as diodes and transistors to complex circuits such as computer chips.

As the name suggests, semiconductors are materials that conduct electricity, but not as easily as conductors. These materials have their conductivity greatly affected by external factors, and can switch between conduction and insulation modes. The most commonly used semiconductor material is silicon.

Semiconductor materials are found in nature. However, when they are in their pure form, they do not have the desired characteristics. They need to go through a process known as doping, where impurities are added to their composition. After this process, two types of semiconductors can be acquired:

• P-Type Semiconductor: It has electron holes, which is why it is called P (positive).

• N-Type Semiconductor: Has excess electrons, hence called N (negative).

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To better understand why there is this lack and excess of electrons, we will need to understand what the atomic bonds between semiconductors are like.

Let's take the most common example, Silicon (Si). A silicon atom has 14 electrons. Of these, 4 are in the valence shell (the outermost shell). Atoms always try to have 8 electrons in their valence shells. Therefore, silicon tends to form crystalline structures, sharing its electrons with the surrounding atoms.

This bond is called a covalent bond, where the same electrons are shared between two atoms.

Each atom shares its 4 electrons with 4 other atoms around it. This way, all atoms end up with 8 electrons in their valence shells. Covalent bonds are strong and make it difficult for electrons to move, i.e., for current to flow.

N-Type Semiconductors

To make N-type semiconductors, that is, with excess electrons, atoms with 5 electrons in the valence layer, for example phosphorus (P), are added as impurities. When doing this, the 4 covalent bonds are still formed, but one electron ends up being left over.

We might think that this material has an easy time sending electrons, but difficulty receiving them.

P-Type Semiconductors

To make P-type semiconductors, that is, with excess electrons, atoms with only 3 electrons in the valence layer, for example boron (B), are added as impurities. By doing this, only 3 covalent bonds are still formed, making the structure need one more electron.

We might think that this material has difficulty sending electrons, but has ease in receiving them.

Applications

The combination of P-type and N-type semiconductors can produce components with desired characteristics for certain applications. The two most common uses of semiconductors are Diodes and Transistors.

Diodes

Diodes are components formed by the junction of N and P type semiconductors, as in the image below. This structure means that the current can only pass in one direction, going from the P material to the N material. The opposite does not happen.

Transistors

NPN transistors are composed of two pieces of N-type material, separated by a P-type material. PNP transistors are the opposite, P-type materials separated by an N-type material. When a current is applied to the intermediate material (called the base), current begins to flow between the other two terminals. Thinking about the ideal transistor, its operation is that of a switch, activated by the current in the base terminal.

Conclusion

In conclusion, semiconductors play a fundamental role in the evolution of modern electronics, being the basis for the development of increasingly sophisticated and efficient devices. Their ability to control the flow of electricity and their unique properties allow the creation of essential components, such as transistors, diodes and integrated circuits, which are fundamental to the functioning of a wide range of technologies.

As demand for faster, more compact, and lower-power devices increases, semiconductor research and innovation will continue to be crucial to the transformation of the electronics industry. The future of electronics is closely linked to the advancement of semiconductor materials, and as new materials are discovered and components are miniaturized, the impact of these advances will be even more profound, opening up new possibilities for society and the global economy.