Crystallinity degradation and defect development in (AlxGa1-x)2O3 thin films with increased Al composition

We systematically analyzed the Al composition dependences of the structural properties of (AlxGa1-x)(2)O-3 thin films grown on ss-Ga2O3 (010) substrates. The crystal structure was characterized by x-ray diffraction, and the surface morphology was observed by reflection highenergy electron diffraction and atomic force microscopy. In the 100-nm-thick thin films, the crystallinity began to degrade and defects appeared on the surface when the Al composition x exceeded about 0.16. The defects developed mainly along the [201] direction and slightly along the [001] direction as x increased. The boundary where the thin film quality changed was close to a critical thickness curve calculated using the Matthews-Blakeslee model assuming the slip system of < 201 > {10 (2) over bar}.