Transistors

Semiconductors have an electrical resistivity that is in between those of good conductors and those of good insulators. Both silicon and germanium, which are the two basic semiconductors, have four electrons in the outermost electron subshell. In formation of the lattice structure of the silicon or germanium, all the valence electrons are involved in the bonding, so the material should be an insulator. However, an unusually small amount of energy is needed to break one …

…can drop out of its cloud and drop into the hole, but this created another new hole in the place where the electron originally was. Because the carriers are positive, this system is referred to as a p-type semiconductor. When the n-type semiconductor is formed, there is a new level formed in between the valence band and the conduction band called the donor level. In a p-type semiconductor, this level is called the acceptor level.