Objective
Heat up or dope a semiconductor crystal and watch the free-electron and hole populations respond - the behaviour behind every computer chip.
The idea
Pure (intrinsic) silicon conducts a little, and more when hot. Add donor atoms and electrons appear for free; add acceptors and holes appear. That doping is the craft of chip-making.
Try this
- 1Raise the temperature and watch carriers multiply.
- 2Add donors and see the electron population leap.
- 3Add acceptors and watch the hole population grow.
- 4Read the intrinsic carrier density and the Fermi level.
Watch for
- Intrinsic carriers grow exponentially with temperature.
- n x p stays fixed at the intrinsic square, whatever the doping.
- Donors push the Fermi level toward the conduction band.
- Extrinsic carriers can outnumber intrinsic ones by millions.