I am following Neamen's book "Semiconductor Physics and Devices". I just could not come to imagine what Ambipolar Diffusion is and feeling very dumb. This concept of both carriers moving together is unintuitive, more so inconceivable to me.

Quoting the textbook, Pg[201].

If a pulse of excess electrons and a pulse of excess holes are created at a particular point in semiconductors with applied electric field, the excess holes and electrons will tend to drift in opposite directions. However, because the electrons and holes are charged particles, any separation will induce an internal electric field between the two sets of particles. This internal electric field will create a force attracting the electrons and holes backwards toward each other. .... The negatively charged electrons and positively charged holes then will drift or diffuse together with single effective mobility and diffusion coefficient. This phenomenon is called Ambipolar Diffusion.

My Ideation.

I assume as he stated earlier that there is low injection. That could mean there is little or no contribution of minorities to begin with. Could it be that these minority carriers are influenced by a few of the majorities and have "clubbed" together with them? I mean, some majority carriers are pulling through these minority carriers. But how could the internal electric field be so much more stronger than the applied electric field such that keeps them together? What happens without low injection?


I thought I'll make quick work of this book but having no prior background in Quantum Mechanics or Solid State Physics is causing great impediment. Also as an Engineering student, these equations are boggling.



Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.