n-type of semiconductor is formed when

An n-type semiconductor is formed when a semiconductor (like silicon or germanium) is doped with an element that has more valence electrons than the semiconductor. These extra electrons can contribute to electrical conductivity.
(1) Silicon doped with phosphorus: Phosphorus has 5 valence electrons, while silicon has 4 valence electrons. When phosphorus is doped into silicon, the extra electron from phosphorus becomes free to move and contribute to electrical conductivity, creating an n-type semiconductor. The extra electron is referred to as a donor electron because it donates its charge to the conduction band.