Analysis of composition fluctuations in AlxGa1−xN

Composition fluctuations in AlxGa1−xN-layers (x=0.25 and 0.35) are investigated on an atomic scale by high-resolution transmission electron microscopy (HRTEM). The samples were grown by plasma induced molecular beam epitaxy on Al2O3 (0001). A strain state analysis of the cross-sectional HRTEM micrographs is performed with the digital analysis of lattice images (DALI) program package. Composition profiles on an atomic scale are derived by the measurement of the distances between intensity maxima positions in the HRTEM image. The analyses revealed different areas in the AlxGa1−xN-layers with either homogeneous or ‘striped’ contrast. In the striped areas the analyses indicate a strong decomposition that leads to the formation of self-organized superlattice structures.