question_answer

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

Answer:

                    The 4 bonding electrons of C, Si or Ge lie, respectively, in the second, third and fourth orbit. Hence, the energy required to take out an electron from these atoms (i.e., ionisation energy \[{{E}_{8}}\] ) will be least for Ge,  followed by Si and highest for C. Hence, the number of free electrons for conduction in Ge and Si are quite significant but negligibly small for C.