Phase separation and gap bowing in zinc-blende InGaN, InAlN, BGaN, and BAlN alloy layers

We present first-principles calculations of the thermodynamic and electronic properties of the zinc-blende ternary InxGa1−xN, InxAl1−xN, BxGa1−xN, and BxAl1−xN alloys. They are based on a generalized quasi-chemical approximation and a pseudopotential-plane-wave method. T–x phase diagrams for the alloys are obtained. We show that due to the large difference in interatomic distances between the binary compounds a significant phase miscibility gap for the alloys is found. In particular for the InxGa1−xN alloy, we show also experimental results obtained from X-ray and resonant Raman scattering measurements, which indicate the presence of an In-rich phase with x≈0.8. For the boron-containing alloy layers we found a very high value for the critical temperature for miscibility, View the MathML source, providing an explanation for the difficulties encountered to grow these materials with higher boron content. The influence of a biaxial strain on phase diagrams, energy gaps and gap bowing of these alloys is also discussed.