A semiconductor is a material with conductivity between a conductor and an insulator. Silicon is the most common, but germanium and gallium arsenide are also used. Semiconductors are the foundation of modern electronics. Transistors, diodes, and integrated circuits are all made from semiconductors. Without them, there would be no computers, no smartphones, no internet. The key property of a semiconductor is that its conductivity can be controlled. By adding impurities, a process called doping, engineers can make it conduct more or less. That control is what makes semiconductor devices possible.

Semiconductors have a band gap, an energy range where no electrons can exist. In a conductor, the band gap is zero. In an insulator, it is large. In a semiconductor, it is small enough that electrons can be excited across it by heat, light, or an electric field. When an electron crosses the band gap, it leaves behind a hole, which acts like a positive charge. Both electrons and holes carry current in a semiconductor. Doping with phosphorus adds extra electrons, creating n-type material. Doping with boron adds holes, creating p-type material. Joining n-type and p-type materials creates a p-n junction, which is the basis of diodes, transistors, and solar cells.

Semiconductor facts

• Definition. Conductivity between conductor and insulator.
• Examples. Silicon, germanium, gallium arsenide.
• Doping. Adding impurities to control conductivity.
• n-type. Extra electrons.
• p-type. Extra holes.

A semiconductor is not the same as a conductor. A conductor conducts easily. A semiconductor conducts only under certain conditions.