Electron – deficit impurities
Silicon or germanium of group 14 can also be doped with elements of group 13 element like B, Al or Ga which contains only three valence electrons.
Three electrons of B form covalent bonds with three electrons of Si.
The fourth electron in Si is extra that remains isolated and creates an electron hole or electron vacancy.
An electron from a neighbouring atom can come and fill the electron hole, but leave an electron hole at its original position resulting in displacement of the electron hole in the direction opposite to that of the electron that filled it.
Under the influence of electric field, electrons would move towards the positively charged plate through electronic holes, but it would appear as if electron holes are positively charged and are moving towards negatively charged plate.
These types of semiconductors are called p-type semiconductors.
