Semiconductors are materials with a conductivity between conductors and insulators, as they have 4 valence electrons.
Elemental semiconductors
Elemental semiconductors are elements in group 14 of the periodic table with 4 valence electrons, such as germanium and silicon. The most common semiconductor used is silicon, used to create silicon crystal lattices.
Compound semiconductors
Compound semiconductors use a pair of elements with an average of 4 valence electrons, such as nitrogen and gallium from group 13 and 15 on the periodic table, or cadmium and tellurium from groups 12 and 16.