The pentavalent impure atoms like phosphorus, arsenic, antimony, bismuth or some other chemical element are used to produce n-type semiconductors. These impure atoms are called donor impurities because they give free electrons to a semiconductor. The doping increases the number of charge carriers in the material for conduction (read more: why do we need doping in semiconductor?). A n-type semiconductor is a lot more conductive than the pure silicon or germanium.