Plastic strain relaxation and alloy instability in epitaxial corundum-phase (Al,Ga)2O3 thin films on r-plane Al2O3

The growth of (AlxGa1−x)2O3 alloy thin films in the corundum phase on r-plane (01.2) Al2O3 substrates is investigated. The growth mode changes from step flow for pseudomorphic layers to three-dimensional growth for strongly relaxed layers. Atomic force microscopy and transmission electron microscopy reveal defects due to prismatic and basal slip. An instability in the growth of the alloy x ≈ 0.6, manifested in doubly-periodic incorporation of Al-rich slabs, is observed.