Semiconductor, the name is widely known, but what is a semiconductor?

Semiconductors have specific electrical properties. A substance that conducts electricity is called a conductor and a substance that does not conduct electricity is called an insulator. A semiconductor is a substance with properties in between.

Electrical conductivity can be expressed by resistivity. Conductors such as gold, silver and copper have low resistance and conduct electricity easily. Insulators such as rubber, glass and ceramic have high resistance and are difficult to pass through. The semiconductor class has properties in between. Their resistivity can vary depending on temperature. At high temperatures, no current passes through them. However, when the temperature is lowered, current easily passes through them.

Semiconductors simply do not conduct electricity. However, when certain elements are added to a semiconductor, current easily passes through them.

Semiconductors consist of individual components known as elemental semiconductors, including the well-known semiconductor materials of silicon. On the other hand, the semiconductor process of two or more compounds is called the upward semiconductor of the compound, and is used in semiconductor lasers, light-emitting diodes, etc.

An atom consists of a nucleus and electrons orbiting it.

Electrons cannot orbit the nucleus at any distance in the atomic space surrounding it, but are allowed only some very special orbits and exist only in certain reunion energy levels. These energies are called energy levels. A small number of atoms cluster together to form crystals and interact in the solid data, and then the energy level spacing becomes so tight that they form energy bands. The band structures of metals, semiconductors, and insulators differ from each other.

In metals, conduction and valence bands are close together and can even be stacked, and Fermi energy (Ef) is located outside. This means that the metal has always had electrons that can move around freely, so it can always carry an electric current. Such electronic scales are free electrons. The flow of these free electrons creates an electric current in the metal.

In semiconductors and insulators, the valence and conduction bands are separated by a stop gap (Eg) of sufficient width, and the Fermi energy (Ef) is between the valence and conduction bands. In order to reach the conduction band, the electron must gain enough energy to skip the band gap. Once that's done, you can stop moving freely.

In a semiconductor at room temperature, the band gap is small, and in the case of infinite conductivity of the semiconductor, there is enough thermal energy for the electrons to fairly easily jump over this gap and stop the transition in the conduction band. At high temperatures, no electron has enough energy to occupy the conduction band, so the charge cannot move. At a relative value of zero, a semiconductor is an ideal insulator. At room temperature, the electron density in the conduction band is not as high as in the metal, so it cannot conduct electricity like the metal. The conductivity of semiconductors is not as good as that of metals, but not as bad as that of insulators. This data is therefore called a semiconductor - representing a semiconductor.

The band gap of an insulator is so large that almost no electron can jump through it. Therefore, the current is not easy to move in the insulator. The difference between an insulator and a semiconductor is the amount of bandgap energy. In an insulator, the bandgap is so large that the energy required for an electron to cross the conduction band is actually large enough. Insulators do not conduct electricity easily. This means that the insulator's conductivity is very poor.

The semiconductor crystal used for IC and so on is 99.999999999% of high purity monocrystal silicon, but in practice when manufacturing circuits, impurities are added to control electrical properties. Depending on the impurities added, they become N-type and P-type semiconductors.

Phosphorus pentavalent (P) or arsenic (As) is added to high-purity silicon for N-type semiconductors. These magazines are called donors. The energy level of the donor is near the conduction band, that is, the energy gap is small. Electrons at that level are then easily excited into the conduction band and help conduct electricity.

On the other hand, the trivalent boron (B) etc. is added to the P-type semiconductor. This is called a receptor. The energy level of the acceptor is close to the valence band. Since there are no electrons here, electrons in the valence band are excited. As a result, holes are formed in the valence band, which contributes to electrical conductivity.