State the process of diffusion
When these two pieces are joined together and suitably treated, they from a pn junction. Moment they form a pn junction, some of the conduction electrons from n type material diffuse over to p-type material and undergo electron-hole recombination with the holes available in valence band. Concurrently holes from p-type material diffuse over to n-type material and undergo hole-electron combination with the electrons available in conduction band. This process is known as diffusion.