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.

Drift Current In a Semiconductor

Anyone looking to summarize what they learn in class? Well i'm going to try to summarize a lot of things I deem complicated, in layman terms for everyone to be able to understand.

So what is drift current? BASICALLY, it is the CURRENT that is created when an electric field (via a voltage source) is applied to a semiconductor.

The applied Electric field causes holes and electrons to accelerate, but in opposite directions. Why? Because electrons always flow in direction opposite to that of an electric field, while the holes follow the electric field.

THEREFORE, giving the electrons AND holes a velocity. For the equations..... you can ask me or look them up somewhere. SO, the TOTAL current becomes a function of the velocity of both the electrons and holes.

MIND YOU, the Velocity, or drift velocity, o both the electron's and holes WILL be different because of the different electron mobility values of each.

If I knew or had time to figure out how to upload pic's and such for this I would. Enjoy! Ask me questions if you desire and I will try my best to answer.