A comprehensive study of p-n junction is necessary to design an electronic device as well as circuits. An electronic device controls the movement of electrons. The study of electronic devices requires a basic understanding of the relationship between electrons and other components of an atom. This leads to knowledge of the differences between conductors, insulators and semiconductors and to an understanding of p-type and n-type semiconductor material. p-n junction is formed by joining p-type and n-type semiconductor materials. So the concept of semiconductor, majority and minority carrier of p-type and n-type semiconductor, doping, depletion region of p-n junction, mobility and conductivity, drift and diffusion current, carrier concentration calculation and Fermi energy level is actually the comprehensive study of p-n junction.