I understand that drift current arises from the application of an external electric field (a voltage) across a piece of conductive material and that when a concentration gradient of charge carriers exists in a semiconductor, it is possible for a current to flow by random thermal motion of these carriers in the absence of an applied voltage. The current so produced is known as diffusion current.
Why is it then that the current flowing through a fully forward-biased diode is called diffusion current instead of drift current? Under this condition, is the majority carrier current (which predominates) not driven by the external forward bias (thereby eliminating the need for thermal excitation associated with diffusion)?
I would be grateful for any clarification please.