What are semiconductors: operation and applications

A semiconductor material It is one that under certain circumstances allows the passage of electric current, while if there are other different ones, it prevents the transmission of electric current and acts as an insulator. However, when we talk about semiconductors in a more colloquial way and referring to the world of the automobile (and electronics in general), we are referring to that series of “chips” and elements that we find in an electronic board and that indeed, semiconductor materials such as silicon are used for its manufacture.

What is a semiconductor?

A semiconductor is all that material that can act both as a conductor allowing the passage of an electric current or as an insulator preventing it according to several factors such as the ambient temperature, the type of atomic structure of the same or the electric or magnetic field to which it is subjected.So, in nature we find several semiconductor materials, among which the silicon (Si) and the germanium (Ge) due to its greater industrial use, although there are also other less widespread ones such as sulfur (S), Boron (B) or cadmium (Cd).

A semiconductor is a material that, depending on several factors, allows the passage of electric current or not, being especially used in the manufacture of electronic components that we find in all technological devices.

Laptop, tablet and smartphone, three everyday devices in which semiconductors are used

However, for this industrial use silicon or germanium is not used in its pure state, which are known as intrinsic semiconductors, but uses the so-called extrinsic semiconductors, which are nothing more than a natural semiconductor with impurities that is obtained through a process of doped.

Why does a semiconductor conduct or not conduct electricity?

Now, what is special about these materials to allow the electric current to pass through sometimes yes, and sometimes not? Leaving aside the chemical and physical precision, we are going to focus on two types of typical semiconductors to illustrate this little explanation: silicon with phosphorus impurities and silicon with aluminum impurities.

If you remember those chemistry classes, we can think of an atom as if it were the Solar System: in the center is the nucleus and electrons rotate around it. Except in the first orbit that can only have two electrons, the others have room for eight of them, and in fact, atoms “want” to always have all their orbits (technically called orbitals) complete in order to reach the most stable state possible.

There are two types of extrinsic semiconductors: negatively charged p-types and positively charged n-types.

Mercedes Eq, Eqs, Interieur, Mbux Hyperscreen Mercedes Eq, Eqs, Interior, Mbux HyperscreenMercedes EQS MBUX multimedia system

In the case of p-type semiconductors, within which the silicon with aluminum impurities, there is a covalent bond in which both atoms share the electrons of their last orbits, which gives rise to a total of seven in that last layer (four from silicon and three from aluminum). The problem is that one more electron is still missing to complete it, and at the moment in which it “captures” it, a material is created negatively charged.

On the contrary, in semiconductors of type nLike silicon with phosphorous impurities, the opposite happens. In this case we have four electrons from silicon and five from phosphorus, so it is necessary to detach an electron to reach that orbit of eight, which gives rise to a material negatively charged.

Semiconductors Polarization TypesDirect and indirect polarization of a semiconductor (J. Pinochet, 2001)

Well, the “magic” takes place when an n-type semiconductor is contacted with another p-type and connected to an electrical source. If the positive pole coincides with the negatively charged type p, it is said that a forward polarization and allows the passage of electricity. On the contrary, if the positive pole is connected to type n, also positively charged, the polarization is reverse and would act as an insulator.

Why is this happening? The most immediate way is to think that in the case of reverse polarization, when connecting the positive pole with the type n of equal polarity “charges of the same sign repel each other”, while the other way around they attract each other and it does allow the circulation of electrons, or what is the same, of an electric current, which is nothing more than a flow of negative charges.

What are semiconductors used for?

The most immediate application of a semiconductor is that of a diode, among which are the well-known light-emitting diodes or LEDs. Thus, depending on the type of goddess, you can modulate and / or rectify a signal to get light, or even convert alternating current into direct current.

However, the most important application of semiconductors lies in the manufacture of transistors. These devices, which can be of the npn or pnp type, allow obtaining an output signal in response to an input and Since their invention in 1947 they have been a small great revolution in consumer electronics by leaving behind the bulkier, expensive and less reliable vacuum tubes.

The main components of consumer electronics (LEDs, transistors, microprocessors …) are manufactured using semiconductor materials.

Thus, by means of a combination of transistors it is possible to create a logical element capable of performing simple mathematical operations (addition, subtraction, multiplication …), which are called logic gates, which, taken to the extreme, becomes the chips and microprocessors that they have all and every one of the electronic devices that surround us, from our smartphone to a simple calculator, through television, the computer, and of course, our car.

Semiconductors Inventors TransistorJohn Bardeen, William Shockley and Walter Brattain invented the bipolar transistor working at Bell Labs (1947)

However, it should be noted that the use of semiconductor materials in electronics predates the invention of the transistor, and it is that at the beginning of the 20th century, devices such as a copper or selenium oxide rectifier manufactured by Westinghouse Electric were already used to convert alternating current into direct current, although as in most technical advances, it was not until the Second War World (1939 – 1945) when the use of these materials in radio and radar devices began to be explored when rescuing the forgotten “Cat whisker detectors”(cat whisker detector), a device that is composed of a metallic filament or whisker that makes contact with a semiconductor crystal (usually pyrite, vitreous silicon or silicon carbide) to detect radio waves.

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