Diffusion current :
Diffusion current is a current in a semiconductor caused by the diffusion of charge carriers (holes and/or electrons). The drift current, by contrast, is due to the motion of charge carriers due to the force exerted on them by an electric field. Diffusion current can be in the same or opposite direction of a drift current. The diffusion current and drift current together are described by the drift–diffusion equation.
Mobility charge carriers :
This is a property of conductor, defined as the ratio of drift velocity to applied electric field in a conductor. Drift velocity of charge carriers in a conductor depends upon two factors, one is the intensity of applied electric field across the conductor and other is one property of the conductor called Mobility of Charge Carrier. In other words, for applied same electric field, on different metallic conductors there will be different drift velocities of electrons. These drift velocities of electrons depend upon a typical property of conductor called mobility of charge carrier.
Given as the ratio of the drift velocity Vdr to the electric field strength E:
