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.