Which of the following is an example of n-type semiconductor?

Germanium doped with phosphorus is an example of n-type semiconductor. Silicon and germanium are group 14 elements having four valence electrons. In their crystals, each atom forms four covalent bonds with its neighbours. When doped with a group 15 element like P or As, which contains five valence electrons, they occupy some of the lattice sites in silicon or germanium crystal. Four out of five electrons are used in the formation of four covalent bonds with the four neighbouring silicon atoms. The fifth electron is extra and becomes delocalised. These delocalised electrons increase the conductivity of doped silicon or germanium. Here, the increase in conductivity is due to the negatively charged electron, hence silicon or germanium doped with electron-rich impurity are called n-type semiconductors.