Semiconductor elements, as the name suggests, are made of semiconductors. To make them useful for practical applications, a process called doping is applied.
The resulting properties can be understood as follows: The more electrons are present in the outer shell of a semiconductor, the more electrons are available for conduction. These electrons are called valence electrons.
Silicon (Si) and germanium (Ge) belong to group IV of the periodic table and therefore have four valence electrons. To increase the conductivity of semiconductors, they are enriched (doped) with foreign atoms that diffuse into the material during production.
- If silicon is doped with an element from group III (e.g., indium, In), there is a high probability that silicon donates one of its valence electrons to the indium atom. In the neighborhood of the adjacent silicon atom, a positive charge arises, called a hole. Such a semiconductor is referred to as a p-type semiconductor. When a voltage is applied, conduction mainly occurs through these holes, which is why this is also called hole conduction.
- If silicon is doped with an element from group V (e.g., phosphorus, P, or arsenic, As), these atoms donate their valence electrons to the silicon. As a result, more negative charges (electrons) are available for conduction, and the conductivity increases. A crystal doped in this way is called an n-type semiconductor.