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Submitted by Anonymous on 13 October 2004 - 2:21am.
Silicon is knwon to be giant covalent structures as like that in diamond. Why can it become a semiconductor?
(I think covalent bonds cannot conduct electricity?)
Also if you have news about replacing pure silicon (Si)n by silicon carbide (SiC)n in semiconductors in computers in order to redce weight (because no ventilation is needed, Silicon Carbide works the same in 0'C and 1500'C), please tell me.
......Rubbish....Rubbish!!!!!!!!! :D :D :D :D
Exactly. Its all about defects, whether they are point defects (places in the lattice where anions or cations should be, or replaced with a different anion/cation) or line defects etc. Though, undoped Silicon becomes conductive without dopants at some temperature where enough "intrinsic defects" are present to conduct electrons. This temperature is probably around 100 to 200C. You can calculate by knowing the bandgap energy(1.2eV for Si), but I forget the equation off hand.
Thats why silicon is used, because the resistance is HIGH, except for where its doped! The undoped regions create huge boundries where the electrons cannot travel. By doping, the resistance is decreased by several orders of magnitude.
In metals, defects typically increase the strength. Bending a paper clip back and forth is a prime example. Notice, after just one or two bends in the same location, the area seems to get stiffer/stronger. Thats because your creating dislocation defects in the lattice.....after a while you create too many, and the area becomes brittle like glass.
Defects are vital to any material
Yes, total purity is useless. Anyway we basically can't make them.