Surface energy minimization struggle between Ge and Si on 4H-SiC(0001)-(3x3)

The Ge growth behaviour on the 3x3 Si-rich surface termination of 4H-SiC(0001) has been investigated in this study. After the deposit of one Ge monolayer at room temperature by molecular beam epitaxy, the film is submitted to isochronal annealing cycles up to 1000°C. A phase separation between Si and Ge is observed during the annealing process accompanied by successive 2D/3D and unusual 3D/2D transitions for both elements. Si and Ge struggle for wetting the bare surface in order to minimize its surface energy. This behaviour seems also to be related to the strain difference induced by the misfit of Si (∼25%) and Ge (∼30%) with the 4H-SiC(0001) substrate.