Formal Definition

A semiconductor is simply a material with electrical conductivity between a Conductor and an Insulator. This is only when that material is atomically pure, with no impurities of other elements that can effect its electronegativity.

The most common element used as a semiconductor is Silicon, followed by Germanium or Gallium Arsenide. Other elements used in the creation of semiconductors, primarily as dopants, are elements such as Boron, Antimony, Carbon, Selenium, Sulfur, and Tellurium.

What defines a good Semiconductor?

For use in industry standard products, or to simply be useful in the context of a basic electrical circuit, a semiconductor must demonstrate a few properties.

1. A symmetrical (redundant), crystal lattice, to achieve stability and predictability.
2. Electrical properties between a conductor and insulator, as explained above.
3. DopingDoped regions of determined N-type or P-type material

These doped regions result in PN Junctions.

A PN Junction is formed with poles of N-Type regions and P-Type regions, hence the term PN Junction. These serve as the foundation of Diodes by providing the ability to act as a switch/gate through a forward or reverse biased applied voltage.

P-type Region

These are typically made of trivalent elements or compounds, possessing only three Valence electrons in their outermost shell. This allows them to serve as “Acceptor” carriers, facilitating electron hole development in the silicon (or other semiconductor material) lattice when a bias is applied to this region. This absence of electrons induces a positive electrical charge, which causes a feedback loop that turns the entire structure into an Insulator.

N-Type Region

These are typically made of pentavalent elements or compounds, possessing five valence electrons in their outermost shell. As only four of these electrons are required to form bonds with the silicon, it leaves one “free” electron to move about. This allows them to serve as “Donor” carriers, facilitating electron mobility, the primary driver of electrical current. This effectively turns the structure into a pathway for electron drift, resulting into the transition into a Conductor.