Hi. I am reading about the pn junction, but I have a question. When the junction is formed the holes in the p-type material close to the junction diffuse across due to the concentration gradient. This leaves the acceptor atoms in the p-type material negatively charged. My question is: when the holes diffuse across from the p-type, are they being filled by electrons from the n-type valence band, or are they being filled by the electrons from the donor atoms of the n-type material (whose energies are close to the n-type conduction band) who are diffusing in the opposite direction? Thanks!