Doping Semiconductors
•The addition of a small percentage of foreign atoms in the regular crystal lattice of silicon or germanium produces dramatic changes in their electrical properties, producing n-type and
p-type semiconductors.
•Pentavalent impurities (5 valence electrons) produce n-type semi-conductors by contributing extra electrons.
•Trivalent impurities  (3 valence electrons) produce p-type semiconductors by producing a "hole" or electron deficiency.