Semiconductors are typically made from elements in Group IV of the periodic table, such as silicon, germanium, and carbon. These elements have four valence electrons, which means that each atom has four electrons that can be shared with neighboring atoms. When two atoms share an electron, they form a covalent bond.
In a pure semiconductor, all of the valence electrons are involved in covalent bonds, so there are no free electrons to carry current. However, if an impurity atom is added to the semiconductor, it can donate or accept an electron, creating a free charge carrier.
Donors are impurities that donate electrons, such as phosphorus and arsenic. Acceptors are impurities that accept electrons, such as boron and gallium. The type of impurity determines the type of semiconductor:
* N-type semiconductors are semiconductors that have been doped with donor impurities, so they have a high concentration of free electrons.
* P-type semiconductors are semiconductors that have been doped with acceptor impurities, so they have a high concentration of free holes (vacant electron positions).
When an N-type semiconductor and a P-type semiconductor are joined together, a PN junction is created. PN junctions are the basic building blocks of transistors and diodes.
Transistors are electronic switches that can be used to amplify or switch electronic signals. Diodes are electronic devices that allow current to flow in only one direction.
Semiconductors are essential to modern electronics. They are used in a wide variety of devices, from simple light switches to complex computers.
