Semiconducting devices

An important area where valence bonds play a fundamental role is in the formation of semiconductors, which are at the heart of today's electronic and computing devices. A semiconductor is a material which is neither a good electrical conductor nor a good electrical insulator. The most famous one, Silicon, is pictured below in a crystal structure.

 

Figure 12.12: Silicon

A particular Silicon atom, with 4 electrons in its outer shell, can share its electrons with 4 of its nearby neighbours, giving a total of 8 electrons. This configuration, like that of the inert gas Argon, is more stable, and this energetically favoured.

Although the electrons in Silicon are bound to the atoms and also bound in these valence bonds, when such a sample is subject to an electrical potential difference, some of these electrons will break free and contribute to a current. This current is not as easy to establish as in a good electrical conductor, but it is definitely easier to do so than in an electrical insulator, where the electrons are more tightly bound.