The role of semiconductors is to form some device structures by changing their local impurity concentrations, which have a certain control effect on the circuit, such as the one-way conduction of diodes, such as the amplification of transistors.
This is something conductors and insulators cannot do. Conductors often appear in circuits as resistors and conductors, and only play the role of voltage or current limiting in the circuit.
Conductor devices (semiconductor devices) usually use different semiconductor materials, using different processes and geometric structures, has developed a wide variety of crystal diodes with different functional uses, and the frequency coverage of crystal diodes can be from low frequency, high frequency, microwave, millimeter wave, infrared to light waves.
The three-terminal device is generally an active device, and the typical representative is a variety of transistors (also known as crystal triode). Transistors can be divided into two categories: bipolar transistor and field-effect transistor. According to different uses, transistors can be divided into power transistors microwave transistors and low noise transistors.
Principle and function: The semiconductor principle is that at very low temperatures, the valence band of the semiconductor is full band (see band theory), after being thermally excited, some electrons in the valence band will cross the forbidden band into the empty band with higher energy, the empty band becomes a conduction band after the presence of electrons in the valence band, and the lack of an electron in the valence band forms a positively charged vacancy, called a hole