Depth-resolved analysis of spontaneous phase separation in the growth of lattice-matched AlInN

We report the detection of phase separation of an Al1−x In x N/GaN heterojunction grown close to lattice-matched conditions (x ∼ 0.18) by means of Rutherford backscattering spectrometry in channelling geometry and high-resolution x-ray diffraction. An initial pseudomorphic growth of the film was found, with good single crystalline quality, the nominal composition and very low strain state. After ∼50 nm, a critical thickness is reached at which the InN molar fraction of the films drops to ∼15% and at the same time the single crystalline quality of the films degrade drastically. This spontaneous effect cannot be ascribed to strain relaxation mechanisms since both techniques show a good single crystalline growth of the ternary under lattice matched conditions.