Why isn't carbon used as a semiconductor ?

Question

We know that silicon and germanium have four electrons in their valence shells and are used as semiconductors.Well Carbon too has four electrons in valence shell, in fact Ge and Si are of the carbon family, but we say that but for Graphite form, Carbon is an insulator ? why ?

Answer 1

carbon has no free electrons available
so it cannot conduct electricitys
in case of germanium and si they have d orbits in the outer shell and they have greater mobility

Answer 2

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RE:
Why isn't carbon used as a semiconductor ?
We know that silicon and germanium have four electrons in their valence shells and are used as semiconductors.Well Carbon too has four electrons in valence shell, in fact Ge and Si are of the carbon family, but we say that but for Graphite form, Carbon is an insulator ? why ?

Answer 3

Carbon, in the form of single-crystal diamond, is used as a semiconductor. Point your search engine at "diamond semiconductor" for examples.

Diamond has a tetrahedral (four-sided pyramid with triangular sides) structure. Each carbon atom has co-valent bonds to four nearest neighbors, effectively filling the outer shell of each atom with eight (shared) electrons. Pure diamond is a very good electrical insulator but also (surprisingly) a very good thermal conductor. Thin slices can be used to build semiconductor devices with excellent heat dissipation.

To make a semiconductor, some of the carbon atoms in the crystal must be replaced with "dopant" elements of the right size to fit into the crystal lattice structure while having either three or five valence electrons to act as acceptors or donors of free electrons wandering around in the lattice. That is, an acceptor atom in the lattice appears as a "hole" that a free electron can drop into. A donor atom has one too many electrons and can give up the extra electron (when sufficient energy in the form of an electrical field is applied) for conduction.

There are two problems with commercial use of diamond semiconductors: (1) flawless single-crystal diamond is expensive to make in sizes large enough for mass production of wafers and (2) getting dopant atoms into the crystal lattice is difficult. Both of these problems are solvable with sufficient economic incentive, which does exist, for high-power microwave (>50 GHz) devices.

Answer 4

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I believe the correct answer is two-fold. First, Carbon is a nonmetal, with very tightly bound electrons, making its intrinsic conduction of electricity rather poor, even under the most ideal of circumstances. Furthermore, semiconductor devices MUST be made of a single crystal, and in this case this would be diamond. I believe it WOULD be possible to make some transistors from diamond, but they would be prohibitively expensive to make, and thus not practical.

Answer 5

In a carbon atom in diamond it cost too much energy to 'excite' it.
Graphite is a rather good conductor!

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