I learned that no charge carriers exist in the depletion region of a PN junction due to the balance between the diffusion current and the drift current due to the electric field created by charged ions. It is understandable that the electric field, which exerts an actual force on charge carriers, prevents diffusion from happening so that no charge carriers due to diffusion current move around in the depletion region. However, it's quite hard to imagine how diffusion, which is simply a random movement of particles according to concentration gradient rather than an actual force, prevents drift current from happening so that no charge carriers move around in the depletion region.
I can imagine two currents being equal in magnitude and opposite in direction. However, in such case, there would still be some charge carriers moving around in the depletion region. So, how exactly do diffusion and drift(electric field) balance each other out so that no charge carriers exist in the depletion region?
Best Answer
Never take a physical model to represent perfection.
We speak of insulators and conductors, but insulators conduct (small) currents, and conductors present (small) resistance to current.
For most practical purposes, the depletion region is an insulator with a negligible concentration of carriers present in it.