Engineering Physics

8.12 Formation of p-n junction

It is not possible to make a single piece of p-n junction by placing a p-type semiconductor material in contact with n-type semiconductor material, because even if the surfaces of contact are very smooth, the area of contact is less at atomic scale. Also, discontinuities in the crystal structure at the junction will be large. The p-n junction can be formed by different methods. They are (i) Grown junction method, (ii) Alloying method and (iii) Diffusion method. These are discribed below.

(i) Grown junction method: In this method, a impure semiconductor crystal is grown from n-type (or p-type) melt to some extent and the melt is counter doped by enough p-type (or n-type) impurity and the crystal is allowed to grow ...