Why does no current flows through a diode if the voltage is applied in the reverse direction?
Answers
Answer:
A diode consists of two materials known as p-type and n-type semiconductors, connected in series which allows current to flow through them differently. In the n-type semiconductor, electrons travel with enough energy such that they're not attached to an atom and are said to be in the conduction energy band. For the p-type semiconductor, electrons "hop" from atom to atom, but lacking the energy to free them, are said to be in the valency energy band.
At the interface between the n-type and p-type materials, a travelling electron has to move either from the n-type to the p-type in one direction, the p-type to the n-type in the other, to continue moving.
Well, an electron moving from the n-type to the p-type material can occur spontaneously because the free electron's energy is released as radiation and it can move to a lower energy state, attached to an atom in the p-type semiconductor. But to move from the p-type to the n-type it has to gain energy from somewhere, and this isn't spontaneous because there is no guarantee of some other process providing this energy.