*Einstein's equation:*

Einstein showed that the parameters, mobility and diffusion coefficients are directly related. Here mobility describes drift of the charge carrier and diffusion coefficient describes diffusion of the charge carriers. Under equilibrium conditions these two forces are equal.

So, in p-type semiconductor drift current is equal to diffusion current of the electrons

Equating both the above equations we get

With the increase in concentration of electrons, pressure energy also increases. The force corresponding to pressure energy gradient is

By equating both the above forces we get,

from the above equation, the ratio of diffusion coefficient of the mobility is directly proportional to its temperature

This relation is called Einstein's relation