Question

7. The atoms below have the following electronegativities: Zn Ga Ge As Se 1.6 1.7 1.9 2.1 2.4 The three isoelectronic (average of 4 valence electrons) semiconductors Ge, GeAs, and ZnSe all have roughly the same size unit cell and internuclear separation (.e. Ge-Ge. Ge-As, and Zn-Se bonds, respectively). Which solid should have the smallest band gap energy? (a) Ge (b) GaAs (C) ZnSe (d) They have the same band gap energies. (e) One cannot compare the band gap energies from the given information,

Answer 1

More will be electronegativity difference between the atoms of solid bond , more will be the attraction between them and hence smaller will be the band gap energy.

Ge - Ge = zero electronegativity difference.

GaAs = 2.1 - 1.7 = 0.4 electronegativity difference.

ZnSe = 2.4 - 1.6 = 0.6 electronegativity difference.

Thus ZnSe will have smallest band gap energy.

Option (C) ZnSe , is the correct answer.