Doping of an Intrinsic Semiconductor: The mixing of a small amount of pentavalent (e.g. phosphorus) or trivalent (e.g., aluminium) substance as impurity in a pure semiconductor (e.g., $\mathit{G}\mathit{e},\mathit{S}\mathit{i}$ ) is called doping. Doping increases the conductivity of a semiconductor.
For doping pure $\mathit{S}\mathit{i},\mathit{G}\mathit{e}$, pentavalent phosphorus is used to convert it to $\mathit{n}$-type semiconductor. Trivalent aluminium is used to convert pure $\mathit{S}\mathit{i},\mathit{G}\mathit{e}$ to $\mathit{p}$-type semiconductor.