Strain effects on InxAl1-xN crystalline quality grown on GaN templates by metalorganic chemical vapor deposition

InxAl1-xN epilayers (similar to 200 nm thick) under different strain states were grown on GaN templates by metalorganic chemical vapor deposition. When the strain is small (0.166 < x < 0.208), InxAl1-xN epilayers are almost fully coherent with the GaN templates, and the surface presents similar characteristic of small hillocks and uniform pits. In the case of large tensile strain, cracks emerged on the surface, but the surface morphology is less influenced compared to the samples with small strain. However, with large compressive strain, the surface roughness dramatically increased and additional smaller pits emerged with partial strain relaxation occurring during growth. In addition, the microstructures were further investigated by transmission electron microscopy. It is demonstrated that even slight relaxation of compressive strain can lead to notable influence on the structural quality and surface morphology of InxAl1-xN films.