What it is a conductor, semiconductor and insulator according band theory

The electric power can be divided into three major groups of materials: conductors, semiconductors and dielectrics. The main difference is that they have different conduction of electric current. In this article, let's talk about the difference of such materials and their behavior in an electric field.

What is the conductor

So, this conductor - material (material, environment), perfectly conducting electrical current. Substance present in so-called free charged particles (electrons or ions) are able to move freely throughout the volume of the substance, and when an electric voltage, a current conductivity.

The main characteristic of the conductor is its "resistance" (R), Measured in ohms or return value called "conduction", is given by:

G = 1 / R

And this value is measured in Siemens.

For conductors applies: the majority of metals, carbon (graphite or carbon), various solutions of salts and acids.

Conductors in which charge transfer is performed mainly by the motion of electrons (electron emission), called conductors of the first kind. If performed due to ions (electrolytes) in charge of moving conductors, the conductors are called second order.

The most widely used metals, because they have the best conductivity and, therefore, have a lower resistance to electric current flowing.

For example, all the supply conductor wires (cords) are made from metals that are conductors.

What is an insulator

Dielectrics are those substances which exhibit large resistance and an electric current is conducted either in its minor amounts.

This is due to the fact that these materials are very few free charge carriers is due to relatively strong atomic bonds. Therefore, when an electric current field in the dielectric is simply not available.

K dielectrics include materials such as glass, porcelain, ceramics, PCB, carbolite, distilled water (no salt impurities), powdered wood, rubber, etc.

Dielectrics also very widely used in everyday life. Wire insulation, electrical housing made of dielectric materials.

But if you create certain conditions, for example, greatly increase the operating voltage, the insulator can become a conductor. Surely you have heard this expression as "insulation breakdown."

The main characteristic of any electrical strength of the dielectric is considered (this value is equal to the breakdown voltage).

What is a semiconductor

As can be seen even from the title semiconductors occupy an intermediate position between the conductors and dielectrics. Semiconductors in the initial state the electric current is not passed, but when applied to a semiconductor material of energy, the semiconductor is converted into a dielectric guide.

Such elements are used in electronics, of which produce transistors, thyristors, diodes, LEDs and the like. D.

Differentiation of substances on the conductors, semiconductors and insulators are explained using Band theory of solids. It is certainly not accepted by all simple, but get to know her extremely desirable.

Band theory of solids

Thus, the difference between dielectrics, conductors and semiconductors can be explained by the band theory. It goes like this:

As is known from the Bohr model of the atom, electrons in an atom placed on certain orbits

In the crystal lattice of the electron orbit Solid inevitable change under the influence of neighboring atoms and electrons. And for this reason, there is a shift of energy levels of electrons retention.

With orbits close to the nucleus of the atom, electrons can move to another level in theory, but now with external orbits that are in a solid blurred into sublevels, the transfer of electrons between them may be rather easy.

And when an electric potential of the electrons, which hop randomly on the outer orbits adjacent atoms acquire a single motion vector, and we observe the electric current.

Therefore, the lower layer where the electrons are freely displaceable, called the conduction band.

Valence band is called the region of allowed energies, and it is under the conduction band.

To moved electron from the valence band to the conduction band, it must cross the so-called bandgap.

Numerically, it is expressed in electron-volts. A semiconductor energy levels, conductors and dielectrics can be schematically represented as follows:

As seen from the figure above the conductor have the forbidden band, i.e. the valence band and the conduction band has a region of overlap. This means that in such a material, even with little power is applied, electrons are beginning to move within the body of the conductor.

At levels between the semiconductor bandgap is present. Its width indicates what energy must be applied to the semiconductor, the electrons began its movement, that is, the current began to flow.

And dielectric forbidden region is so wide that the transfer of electrons from the valence to the ongoing area practically excluded. Since it requires considerable energy to overcome this barrier, which would cause the destruction of the dielectric.

conclusion

That's all I wanted to tell you about dielectrics, conductors and semiconductors. If you article was interesting and useful, you will appreciate it. And thank you for your attention!