Silicon, Circuits, and the Digital Revolution

Doping Semiconductors - Donors

• What happens if we add a few atoms of gallium?
• Gallium has one fewer valence electron than silicon
  -- when it is placed substitutionally in the lattice for a Si atom only three of the neighboring neighboring Si atoms are successfully bound,
  -- a hole remains, which also aids conduction since electrons may now move more freely through the lattice, "jumping" into a hole and leaving a hole behind to be filled.

• In the band structure picture, impurity states are created much closer to the valence band.
• These states are known as acceptors, since they can accept electrons from the valence band.
• Again, it is much easier to "liberate" the electron for conduction at lower thermal energy.
• A semiconductor doped with acceptors is known as a "p-type" semiconductor. (p for positive charge carrier)

Comments, suggestions, or requests to ghw@udel.edu. "http://www.physics.udel.edu/~watson/scen103/colloq2000/doping-acceptors.html" Last updated April 20, 2000. © George Watson, Univ. of Delaware, 2000.