An Atomic Description of Silicon. All matter is composed of atoms. Atoms, in turn, are composed of positively charged protons, negatively charged electrons, and neutral neutrons. The protons and neutrons, which are of approximately equal size, comprise the close-packed central "nucleus" of the atom, where almost all of the mass of the atom is located. The much lighter electrons orbit the nucleus at very high velocities. Although the atom is built from oppositely charged particles, its overall charge is neutral because it contains an equal number of positive protons and negative electrons.

The electrons orbit the nucleus at different distances, depending on their energy level; an electron with less energy orbits close to the nucleus, whereas one of greater energy orbits farther away. The electrons farthest from the nucleus interact with those of neighboring atoms to determine the way solid structures are formed.

The silicon atom has 14 electrons, but their natural orbital arrangement allows only the outer four of these to be given to, accepted from, or shared with other atoms. These outer four electrons, called "valence" electrons, play an important role in the photovoltaic effect.

As depicted in this simplified diagram, silicon has 14 electrons. The four electrons that orbit the nucleus in the outermost, or "valence," energy level are given to, accepted from, or shared with other atoms.

More:

• An Atomic Description of Silicon
• The Silicon Molecule
• Introducing Phosphorous
• Introducing Boron
• Other Semiconductor Materials
• Absorption and Conduction