Understanding p-n junction dynamics

In p-n junctions there are two opposing currents. One is a drift current associated with an electric field in the interfacial region. The other is a diffusion current associated with the fact that n and p are not the same everywhere, but rather vary as a function of distance from the interface. This video talks about those two types of currents and introduces the scattering rate approximation which we use to simplify each of them.
 

This second video looks at the nature of the interface where the p-doped material and the n-doped material meet. In includes a discussion of depletion and how that leads to space charge and a non-zero "built in" electric field in the vicinity of the interface. This video derives the x dependence of that electric field in the context of the depletion approximation ansatz.



In the third video we discuss the electric potential, how one can get that from the electric field. One can then use the electric potential to establish the nature of the band-bending that occurs in the vicinity of the interface. From the bent bands one can obtain n(x). One can then calculate the two electron currents that are important near the interface: 1) the drift current which is proportional to n(x) times the electric field, and, 2) the diffusion current which depends on the derivative of n(x) with respect to x.