Band gap of Si,Ge,C

Question

Band gap of si,Ge,C. Give reason how carbon have large value?

Answer 1

Hi Prashant!

 

The origins of band structure in crystalline solids lies in multiple factors.  In fact, it changes even for different crystalline forms of the same elements (pure carbon, graphite, and diamond, for example, have different band structures and different electrical and thermal properties because of it).

 

But, if we want to give one reason why pure carbon has a large band gap (and can be used as an insulator), a main factor would be how strong carbon bonds to itself.  The band gap most directly relates to how easily electrons can be promoted from the valence band (where they are bound to the crystalline structure) to the conduction band (where they are free to move and transfer electrical and thermal energy).  Pure carbon tends to be a pretty stable element, and forms strong single, double, and triple bonds with itself.  It thus becomes more difficult for electrons to break free and move into the conduction band.  

 

This can be tracked by carbon's electronegativity, which is half a unit higher (a significant difference) on the Pauling scale compared to Si and Ge.

 

This is a simplification, of course, as band gaps arise from the complex interactions of atoms in a crystal.  But as a single reason, it is one of the prominent ones.

 

I hope this helps!  If you want to talk more about it, just let me know.