What Are Semiconductors?

What Are Semiconductors?

Most of today’s electronic products, such as computers, mobile phones, or digital tape recorders, have a very close connection with semiconductors. So, what is a semiconductor? The semiconductor definition can be illustrated from different perspectives. Firstly, let’s know what are the semiconductor materials. Please see the table of common semiconductor materials below:

TypeGroupMaterial
Simple substance/Element semiconductorSi, Ge, Se
Binary compound semiconductorIII-V groupGaN, GaP, GaAs, AlN, InP
II-VI groupZnO, CdS, CdSe, CdTe
IV-IV groupSiC, C
IV-VI groupPbTe
V-VI groupBi2Te3
III- VI groupGaTe, Ga2O3
I-VI groupCu2O
Ternary Compound SemiconductorI-III-VI groupCulnSe2
II-IV-V groupCdSnAs2
I-VIII-VI groupCuFeS2
PerovskiteCaTiO3
OthersMultiple compoundsInGaZnO
Impurity semiconductor

Solid solution semiconductor

Commonly used elements:

First subfamily,

Second subfamily,

The third to sixth main families

 

Among various semiconductor materials listed in the table, silicon is the most influential in commercial applications , which can be offered by PAM-XIAMEN. To know the semiconductor materials well, definitions for semiconductors are introduced as follows:

1. Semiconductor Definition in Terms of Electrical Conductivity and Solid Property

In the first statement, there are three types of solids in the world: conductors, semiconductors, and insulators. For semiconductor definition electricity, it refers to solids with conductivity between conductors and insulators at room temperature. We usually call solids with poor conductivity as insulators, such as coal, artificial crystals, amber, ceramics, etc; and metals with better conductivity, such as gold, silver, copper, iron, tin, aluminum, etc., are called conductors.

This is a qualitative statement. If quantitative analysis is required, the calibration of conductivity is defined by Ohm’s law U=IR. U is the voltage across the material, I is the conduction current of the material, and R is the resistance shown by the material; R =ρl/S is used to eliminate the influence of material shape.ρ stands for the resistivity to be measured, l is the length of the material, and S is the cross-sectional area of the material.

The representative materials of conductors are various metals, and the dimension of resistivity at room temperature is 10^-8Ωm;

The resistivity of semiconductor silicon is 10^6Ωm;

The resistivity of the insulator paper is 10^6 to 10^14Ωm.

From the above explanation, the difference in resistivity between an insulator and a semiconductor is not as great as the difference between a semiconductor and a conductor. Silicon can also be regarded as an insulator. Therefore, it is meaningless to discuss semiconductors with the resistivity at room temperature.

2. Define Semiconductor From the Perspective of Conductivity

The second argument is the semiconductor definition physics defined from a deeper level of conductivity: the resistivity of a conductor increases with temperature, while the resistivity of semiconductors decreases with temperature. Generally speaking, the carriers are electrons and holes. The movement of electrons actually exists, and the movement of holes is actually the equivalent of restraining the movement of electrons.

Because the lattice/electron interacts with conductive particles (electrons, etc.), resistance is hindering the movement of conductive particles. The main factor that determines the resistivity is the density of conductive particles-electrons. The electron density of a single metal is 10^23/cm3. When the temperature rises, the interaction between the electrons increases, so the resistivity rises. As the temperature rises, the electrons in the semiconductor will change from being bound by the crystal lattice to conductive free electrons, and the resistivity will drop.

However, the semiconductor definition of physics is not complete.

For a single metal, the resistivity increases with the increase of temperature, which is a linear relationship; and the alloys of different metals can obtain the standard resistance, whose resistivity hardly changes with the change of temperature. While the resistivity of insulators and semiconductors are both decreasing with the increase of temperature, which is not a linear relationship. It refers to the undoped semiconductor—intrinsic semiconductor.

You can see that semiconductors and insulators are actually conflated, and the actual use of semiconductor materials will not characterize this property.

3. Explain Semiconductor through Energy Band Theory

Further analysis and semiconductor definition physics below is from the aspect of conduction band.

3.1 Energy Band of Semiconductor

The valence electrons in the conductor are not full of the energy band, while the valence electrons of the semiconductor and insulator completely occupy the energy band. Since the energy band is completely filled, it must transition to the previous energy band to conduct electricity. Such a semiconductor is called intrinsic semiconductor. The middle is the band gap, and the corresponding energy is called the band gap width. However, if the band gap width is smaller, electrons can still cross the band gap / forbidden gap under the action of room temperature/voltage, which can move freely and have conductivity. Therefore, materials with a band gap of about 2eV are called semiconductors. Actually, with the introduction of the third generation of semiconductors (wide band gap semiconductors), the corresponding AlN with a band gap of 6.2eV is regarded as a semiconductor.

In fact, there is no essential difference between semiconductors and insulators. On the opposite side of the conductor is a non-conductor. Non-conductor represents a variety of situations: under what temperature, what pressure, what voltage, what magnetic field, etc, which can be used to judge a conductor or not. As long as there is a band gap, it is an insulator. However, under certain external conditions, an insulator can be converted into a conductor. If this condition is available and can be used in the electronic and electrical industry, this type of insulator is a semiconductor.

Semi-insulator has the same meaning as semiconductors. The literal translation should be a quasi-insulator, which can be converted into a conductor. The resistivity of high-purity silicon carbide is extremely low, but injecting some particles can change the local conductivity. (Note: Immature understanding.)

3.2 The Application of Energy Band

As for the application, we will not use the energy band of one material alone, but combine or dope different materials to form the energy band structure we need. For example, a PN junction composed of a P-type semiconductor and an N-type semiconductor; a MOSFET composed of P-type semiconductor + N-type semiconductor + conductor + insulator.

The most suitable semiconductor definition conduction band is a substance with a band gap / forbidden gap. The semiconductor material is a material whose band gap can be used to serve production and life. Not all band gaps can be used, and even if they can be used, Only the semiconductor material with band gap have more advantages than these commercially available materials, can the material be used.

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