Why is the band gap in alloys such as GaAs less?

[Engineer1]

TL;DR

Why is band gap in alloys such as GaAs less in comparison with intrinsic semiconductor crystals, such as Silicon?

In pure crystals,such as,in silicon and germanium,the band gap is more than that in compound semiconductors,such as,GaAs.Why is that so.

 

[phyzguy]

This is simply wrong. Try looking at the table of band gaps at this Wikipedia page. Silicon is 1.14 eV. GaAs is 1.43 eV. GaN is 3.4 eV. Other compound semiconductors have band gaps less than silicon.