Semiconductor refers to a material whose conductivity can be controlled from insulator to conductor. No matter from the perspective of science and technology or economic development, the importance of semiconductors is very great. Most of today's electronic products, such as computers, mobile phones or digital recorders, are closely related to semiconductors. Common semiconductor materials include silicon, germanium, gallium arsenide, etc., and silicon is one of the most influential semiconductor materials in commercial applications.
The conductivity of a material is determined by the number of electrons contained in the conduction band. When the electrons get energy from the valence band and jump to the conductive band, the electrons can move freely between the bands and conduct electricity. The energy gap between the conductive band and the valence band of common metal materials is very small. At room temperature, electrons are easy to obtain energy and jump to the conductive band to conduct electricity. However, insulating materials are difficult to jump to the conductive band because of the large energy gap (usually greater than 9 electron volts), so they cannot conduct electricity.
The energy gap of a general semiconductor material is about 1 to 3 electron volts, which is between a conductor and an insulator. Therefore, the material can conduct electricity as long as it is excited by energy under appropriate conditions or the spacing of its energy gap is changed.
Semiconductors transmit current through electron conduction or hole conduction. The way of electron conduction is similar to the flow of current in copper wire, that is, under the action of electric field, highly ionized atoms transfer excess electrons to the direction with low degree of negative ionization. Hole conduction refers to the current (generally referred to as positive current) formed by the "holes" formed by the absence of electrons outside the atomic nucleus in positively ionized materials. Under the action of an electric field, the holes are filled by a small number of electrons and cause the holes to move.
