A compound semiconductor is a semiconductor compound composed of elements from two or more different groups of the periodic table. These semiconductors typically form in groups 13–15 (old groups III–V), for example of elements from group 13 (old group III, boron, aluminium, gallium, indium) and from group 15 (old group V, nitrogen, phosphorus, arsenic, antimony, bismuth). The range of possible formulae is quite broad because these elements can form binary (two elements, e.g. gallium(III) arsenide (GaAs)), ternary (three elements, e.g. indium gallium arsenide (InGaAs)) and quaternary (four elements, e.g. aluminium gallium indium phosphide (AlInGaP)) alloys.