What type of semiconductor material contains more free electrons than pure germanium or silicon crystals?

An N-type semiconductor is created by doping pure silicon or germanium with an element that has five valence electrons, such as phosphorus, arsenic, or antimony. When this impurity is added to the crystal lattice, four of the electrons form bonds, leaving the fifth electron unattached and free to move. This additional negatively charged electron increases the overall electrical conductivity of the material. Because the doping process introduces these extra electrons, an N-type material contains significantly more free electrons than a pure, undoped semiconductor crystal. The 'N' in N-type effectively stands for 'Negative,' which is a handy way to remember that the majority charge carriers in this material are negatively charged free electrons. Conversely, P-type materials have a deficit of electrons.