Question

Carbon, silicon and germanium have four valence electrons each. At room temperature which one of the following statements is most appropriate?

• A. The number of free conduction electrons is significant in $C$ but small in $Si$ and $Ge$
• B. The number of free conduction electrons is negligible small in all the three
• C. The number of free electrons for conduction is significant in all the three
• D. The number of free electrons for conduction is significant only in $Si$ and $Ge$ but small in $C$

Answer 1

Answer: (D)

$C$, Si and Ge have the same lattice structure and their valence electrons are $4$ .
For $C$, these electrons are in the second orbit, for $Si$ it is third and germanium it is the fourth orbit. In solid state, higher the orbit, greater the possibility of overlapping of energy bands.
Ionization energies are also less therefore $Ge$ has more conductivity compared to $Si$.
Both are semiconductors. Carbon is an insulator.