Ed's Radio (AA6ED) – Semiconductors


The term Semiconductor refers to material that does not conduct well, but is not an insulator either. Semiconductors, such as silicon and germanium, have four electrons in their valence (outermost) shell — halfway to the desired eight electrons for stability. Because of this, a silicon atom, for example, will form a covalent bond with four other silicon atoms to fill its valence shell.

Adding impurities to the semiconductor material (a process called doping) changes its electrical characteristics. Doping material comes in two types. If the material contains five electrons in its valence shell, it is called N‐type material because it contains an excess of negative charges. N‐type material is typically doped with antimony, arsenic, or phosphorus. If the doping material contains only three electrons in its valence shell, such as aluminum, boron, or gallium, it is called P‐type material because it contains an excess of positive charges (called hole charges).

Hole Charges

A hole charge is a term used in electrical engineering that occurs when talking about P‐type semiconductor material. A hole charge is positive, but is not a proton. Protons are stable and locked inside the nucleus of an atom. A hole charge is an absence of an electron. It is a position in an atom where an electron could exist but doesn't. Think of it as an empty chair at a dinner table. Someone could sit there but it is currently empty. If an extra person entered the room, they would be naturally "attracted" to the empty chair, just as an electron is "attracted" to the hole charge.

Hole current flows in the direction of conventional current. This is opposite of electron flow because hole charges are positive. Hole current only flows in P‐type semiconductor material. The actual current flow through N‐type material is electron flow.

Next: Diodes