Microscopic crystalline structure of a thick AlN film grown on a trench-patterned AlN/α-Al2O3 template

• We develop a microstructure analysis method of AlN films by X-ray microdiffraction.
• Microscopic crystalline structure of thick AlN film is anisotropic.
• Microscopic crystalline structure of AlN film is periodic in the [112¯0] direction.
• Strain relaxation along the growth direction causes the AlN crystal domain tilting.
• Inhomogeneous defect distribution induces lattice tilting and strain fluctuations.

The microscopic crystalline structure (MCS) such as domain texturing, lattice tilting fluctuation and strain fluctuation in thick AlN films grown on trench-patterned AlN/α-Al2O3 templates was clarified by utilizing position-dependent X-ray microdiffraction measurements in combination with transmission electron microscopy observations. The results clearly demonstrate that the trench-patterned templates have a strong influence on the MCS in the thick AlN films. The MCS is anisotropic between the [112¯0] and [11¯00] directions. Periodic domain texturing was observed along the [112¯0] direction, corresponding to the periodicity of the patterning pitch of the template. Submicron crystal domains are tilted at different angles to the [112¯0] direction, and the crystal domain tilting becomes larger in the void-containing trench regions than in the terrace regions. This generates the periodicity in lattice tilting fluctuation and strain fluctuation along the [112¯0] direction. These were found to be caused primarily by two factors; one of which being the elastic strain relaxation that depends on the growth direction in the terrace regions, and the other being the inhomogeneity in distribution and morphology of dislocations that have Burgers vectors with a screw component in the void-containing trench regions.