Variation of Energy Bands with Alloy Composition

1. The  band  structures  of  III-V  ternary  and  quaternary  compounds  modifies  as  their composition is varied.
2. There are 3 valleys in the conduction band: Γ (at k = 0), L, and X.
3. In GaAs, the Γ valley has the minimum energy (direct with  Eg = 1.43 eV) along with very few electrons residing in L and X valleys (apart from for high field excitations).
4. In AlAs, the X valley has minimum energy (indirect along with Eg = 2.16 eV).

Figure: The E-k diagram of (a) GaAs and (b) AlAs, showing the three valleys (L, Γ, and X) in the conduction band.