I have always argued to myself that drift and diffusion components of the current though a p-n-junction cancel for each type of carrier because any electron diffusing from n into p will sooner or later require the same electron to drift back. (And analogously for holes).
However, it now seems to me that the generation of EHPs (electron-hole-pairs) profoundly contributes to the drift current:
"The supply of minority carriers on each side of the junction required to participate in the drift component of current is generated by thermal excitation of electron-hole pairs." (In "Solid-State-Electronic Devices" , Streetman and Banerjee)
In thermal equilibrium, that implies an equal amount of recombination events.
Anyway, one can imagine an EHP being generated on the p-side, with the electron drifting and the hole diffusing to the n-side, where thy recombine. In that scenario, there is no hole drift and no electron diffusion, but hole diffusion and electron drift.
So, how in earth does one dare to argue that "the drift and diffusion components must cancel for each type of carrier"?
I feel like I am missing the real argument.