Phase separation and atomic ordering in mixed III nitride layers

It is demonstrated that group III atomic species in the mixed III nitrides, differing in their covalent tetrahedral radii, are not distributed at random on their sub-lattice. Two types of deviations from randomness are observed: phase separation and atomic ordering. Phase separation lowers the strain energy of the layer. The absence of phase separation in InGaN quantum wells is attributed to the stress imposed by the GaN barrier layers. Atomic ordering doubles the periodicity along the [0 0 0 1] direction.