Silicon, Circuits, and the Digital Revolution

Doping Semiconductors - Donors

• What happens if we add a few atoms of arsenic?
  Recall the periodic table and electronic configurations:
  

  Element:		Configuration:
  Silicon		[neon] 3s2 3p2
  Gallium		[argon] 4s2 4p1
  Arsenic		[argon] 4s2 4p3

• Arsenic has one more valence electron than silicon
  -- when it is placed substitutionally in the lattice for a Si atom four of the valence electrons bind to neighboring Si atoms, the one left over becomes free for conduction

• In the band structure picture, impurity states are created much closer to the conduction band
• These states are known as donors, since they "donate" electrons to the conduction band.
• It is much easier to "liberate" the electron for conduction at lower thermal energy.
• A semiconductor doped with donors is known as an "n-type" semiconductor. (n for negative charge carrier)

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