2. First Brillouin zone of FCC lattice and the band diagram (Do you see any gaps?)

3. Here is one with a gap !
This type of bandgap is called an “indirect bandgap” material.
Band diagram of silicon

4. It is all about exciting electrons from the valence band.

5. P-type semiconductor: Si doped with a 3 valence element that substitutes Si atoms in the lattice. Carriers are mainly holes
N-type semiconductor: Si doped with a 5 valence element that substitutes Si atoms in the lattice. Carriers are electrons.

6. Facts:
Doping a semiconductor with a second element that has excess or fewer valence electrons than the number of bonds in pure Si changes the carrier amount and their types.
How “semiconduction” is manipulated has nothing to do with only single n-doped pr p-doped crystal.
When a p-doped crystal is brought into contact with an n-doped one, interesting things happen.
These “interesting things” determine how a transistor functions…
Every transistor is, this way or that way, a p-n junction.

8. Before any potential applied
After potential applied