Doping of pentavalent atom with hexavalent atom We know that a tetra valent element can be a semiconductor and doping of pentavalent and trivalent impurities would give a extrinsic semiconductor.
I got a question now. Can we use an element of valency 5 and doping it with another element of valency 6 . will it give us a N-type semiconductor? because we are using an atom of valency 4 and doping it with 5 to give N-type semiconductor.Could anyone explain why we use only tetravalent atoms. and also why dont we use carbon even though its a tetravalent atom.Please explain me in detail.Thanks.
 A: Yes, you can certainly use group VI elements for n-type doping in semiconductors which contain pentavalent atoms. Some examples are: Sulfur, Selenium, and Tellurium which turn Gallium Arsenide into an n-type semiconductor. However, Gallium Arsenide is a compound semiconductor; and I don't think elements in groups II, III, V, VI can form semiconductors by themselves (i.e. without combining with elements from other groups). You can see a list of semiconductors here:
http://en.wikipedia.org/wiki/List_of_semiconductor_materials
You can see that there are mostly group IV, III-V, and II-VI present.
As Ron said, carbon, in diamond form, would be pretty expensive. However, in 2004 graphene was found to be another allotrope of carbon; it is turning out to be a promising candidate for electronics. The electron mobility is orders of magnitude better than Silicon. As a matter of fact, it is better than the best semiconductors (such as InSb) known so far. Graphene, unlike diamond, is very cheap. You produce some of it every time you write with a pencil! Also, you can dope graphene the same way as silicon; i.e. with group V elements to become an n-type semiconductor. But the interesting thing about graphene is that you can also dope it electrostatically. 
A: The purpose of performing doping is to make a metalloid a semiconductor, we can use any Pentavalent hexavalent, but both should be metalliods because if the element is a conductor then it'd obviously pass current and nonmetal wouldn't pass through at any so thats why the element should be metalloid.
