Bowing parameters for zinc-blende Al1−xGaxN and Ga1−xInxN

First-principles calculations have been used to determine bowing parameters for disordered zinc-blende Al1−xGaxN and Ga1−xInxN. The direct transition at Γ is found to bow downward for both materials with parameters +0.53 and +1.02 eV, respectively, while the Γ-to-X transition bows upward for Al1−xGaxN (parameter −0.10 eV) and downward for Ga1−xInxN (parameter +0.38 eV). The similarity of the calculated bulk zinc-blende and wurtzite Γ-point transitions also allows estimates to be made of the energy gap versus composition for wurtzite alloys.