Question

$C,Si$, and $Ge$ have the same lattice structure. Why is $C$ insulator while $Si$ and $Ge$ intrinsic semiconductors?

Answer 1

• Carbon$\left(C\right)$, Silicone$\left(Si\right)$, and Germenaium$\left(Ge\right)$ are the elements of the carbon family.
• Each element of the carbon family has $4-$ electrons in the valence shell.
• Since the valence shell increase down the group. Hence, the energy gap of $\left(Ge\right)=0.72eV,Si=1.1eVandGe=5.54eV$ are in the decreasing order.
• So, the energy gap is least for the Germanium$\left(Ge\right)$. So, it is easy to remove an electron from the valence shell of $Ge$ and $Ge$ is an intrinsic semiconductor.
• Due to this the no. of free electrons for conduction will be significant in $Ge$ and $Si$, but will be negligibly small for $C$. That is why $C$ is an insulator while $Si$ and $Ge$ are intrinsic semiconductors