Epitaxial growth of Al-Cr-N thin films on MgO(111)

Cubic rock salt structure Al0.60Cr0.40N and Al0.68Cr0.32N films of different thicknesses were grown epitaxially onto MgO(111) substrates by reactive unbalanced magnetron sputtering at 500°C. Rutherford backscattering spectroscopy reveals stoichiometric nitrides with Al/Cr ratios close to the ones of the used compound targets of 60/40 and 70/30. High resolution xray diffraction proves epitaxial growth over the whole film thickness up to thicknesses of ~1.8 μm. Reciprocal space maps and selected area electron diffraction show that the AlxCr1-xN films grow fully relaxed. Scanning and transmission electron microscopy imaging reveals columnar microstructures with column widths between 12–16 nm and {001} surface faceting on individual columns. The fully relaxed growth and the columnar structure can be attributed to limited ad-atom mobility on the initial AlxCr1-xN(111) growth surface.