A semiconductor has electrical conductivity between that of a conductor and an insulator. Semiconductors differ from metals in their characteristic property of decreasing electrical resistivity with increasing temperature.Semiconductors can also display properties of passing current more easily in one direction than the other, and sensitivity to light. Because the conductive properties of a semiconductor can be modified by controlled addition of impurities or by the application of electical fields or light, semiconductors are very useful devices for amplification of signals, switching, and energy conversion. The comprehensive theory of semiconductors relies on the principles of quantum physics to explain the motions of electrons through a lattice of atoms.
Current conduction in a semiconductor occurs via free electrons and holes, collectively known as charge carriers. Adding a small amount of impurity atoms greatly increases the number of charge carriers within it. When a doped semiconductor contains excess holes it is called “p-type”, and when it contains excess free electrons it is known as “n-type”. The semiconductor material used in devices is doped under highly controlled conditions to precisely control the location and concentration of p- and n-type dopants. A single semiconductor crystal can have multiple P and N type regions; the p-n junctions betweeen these regions have many useful electronic properties.
Silicon carbide material having holes as the majority current carriers. Holes have positive charge (p). Doping with the impurity Boron creates p-type material.