What is the Diffusion Constant? (Semiconductors)

I would say the Diffusion Constant is much like the value for the mobility of holes and electrons. It is merely an indicator of how well a particular charge carrier will diffuse across a semiconductor.

Please take note; the Diffusion does not necessarily involve an applied electric field. Most textbooks will introduce this by simply saying that "magically" there is a greater number of holes (or electrons) on one side and then they diffuse to the side with the least concentration. The concentration of charge carriers THEN, is NOW defined by location, usually "x", within the semiconductor.

The current and current density is dependent on charge carrier concentration, Diffusion constant, and charge q.