What is a semiconductor?

Germanium, silicon, selenium, gallium arsenide, many metal oxides and metal sulfides. Semiconductors with conductivity between conductor and insulator are called semiconductors.

Semiconductors have some special properties. For example, a thermistor for automatic control can be made by using the relationship between the resistivity of the semiconductor and the temperature; Using its photosensitive characteristics, it can be made into photosensitive elements for automatic control, such as photovoltaic cells, photovoltaic cells, photoresistors and so on.

Semiconductors have another most important characteristic. If a small amount of impurities are properly doped in pure semiconductor, its conductivity will increase by millions of times. This characteristic can be used to manufacture various semiconductor devices, such as semiconductor diodes and triodes.

When one side of a semiconductor is made into a P-type region and the other side is made into an N-type region, a thin layer with special properties is formed near the junction, which is generally called a PN junction. The upper part of the figure is divided into carrier diffusion on both sides of the interface between p-type semiconductor and n-type semiconductor (represented by black arrows). The middle part is the formation process of PN junction, which indicates that the diffusion effect of carriers is greater than the drift effect (the blue arrow indicates the direction of built-in electric field). The lower part is the formation of PN junction. Represents the dynamic balance between diffusion and drift.