Carbon, silicon and germanium have four valence electrons each. These are characterised by valence and conduction bands separated by energy band gap respectively (E_g)_C, (E_g)_Si and (E_g)_Ge. Which of the following statements is true?

Question

Accepted Answer

(1) (E_g)_C > (E_g)_Si > (E_g)_Ge. Idea: all three elements are tetravalent and build the same kind of covalent crystal, but going down the group the atoms get larger and the bonds weaker, so the forbidden gap shrinks. Carbon in the diamond structure has the smallest atoms and the strongest bonds: (E_g)_C≈5.4 eV, wide enough to make diamond an insulator. Silicon comes next: (E_g)_Si≈1.1 eV, narrow enough for thermal energy to lift a few electrons across. Germanium has the largest atoms of the three and the narrowest gap, (E_g)_Ge≈0.72 eV, so it has the most carriers at room temperature. So (E_g)_C > (E_g)_Si > (E_g)_Ge.

Carbon, silicon and germanium have four valence electrons each. These are characterised by valence and conduction bands separated by energy band gap respectively (E_g)_C, (E_g)_Si and (E_g)_Ge. Which of the following statements is true?

Step-by-step solution

Why the other options are wrong