In a diode, or PN junction, you have two regions:
- region P with an excess of holes: the material is doped with atoms having 3 electrons instead of 4
- region N with an excess of electron: the material is doped with atoms having 5 electrons instead of 4
Each two regions are neutral but when we place them side by side, some electrons and some holes diffuse from one region to the other: it creates a depletion region with no free charge. Once the charges move, it creates a negative potential barrier in the P region and a positive potential barrier in the N region; this potential prevents the diffusion of the charges: it creates a "drift current".
You can polarize the PN junction in two way: direct polarization and reverse polarization.
In the direct polarization you apply a positive voltage to the P region: holes and electrons can now enter to the depletion zone (thanks to this positive potential) and the depletion zone and the potential barrier are reduced.
In the reverse polarization the potential barrier and the depletion zone are increased.
In conclusion, if you consider electrons, the current flows from - to +. This is also the case of the second video: a negative potential is applied to the N zone, while a positive one to the P zone. The electrons flows from N to P (from - to +).