Silicon, Circuits, and the Digital Revolution
Insulator or Semiconductor?
- Viewgraph of energy levels as a function of atom separation for Group 4
-- four valence electrons
- Model of crystal structure (Bring ball-and-stick model to class.)
-- covalent bonding to four nearest-neighbors
----- sharing of electrons
Unit Cell from Education
Applets in Solid State Materials,
Center for Active Learning
of Microelctronics and Photonics at SUNY
- Relative size of bandgap
-- the energy separation between valence and conduction bands
||(at room temp.)
||[helium] 2s2 2p2
||[neon] 3s2 3p2
||[argon] 4s2 4p2
to photon energies, recall:
- Diamond is considered to be an insulator,
whereas Se, Si, and Ge are considered to be semiconductors.
- Diamond is transparent to visible light, Si and Ge are not;
can be explained with relative band gap energies.
-- optical absorption; energy or photon is absorbed by electron and photon
-- (Examine wafer of silicon.)
- In general, thermal electrons still cannot "jump" bandgap in pure semiconducting
- Photons of sufficent energy can "promote" conduction electrons.
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Last updated April 19, 2000.
© George Watson, Univ. of Delaware, 2000.