Nucleation and growth of GeTe films on KCl and SnTe substrates

The nucleation and growth of GeTe films on KCl or SnTe substrates is found to follow the same mechanism on both substrates. Nucleation occurs through the formation of three-dimensional nuclei of almost equal sizes, bounded by edges along the 110] and 1$\text{1}$0] directions. The growth continues through the lateral extension of the nuclei. The overgrowth layer is anisotropic strainwise, due to the difference in lattice misfit along 110] and 1$\text{1}$0]. This angular misfit is responsible for an increase in the equilibrium energy by 5%. The excess strain is accommodated by misfit dislocations forming a network parallel to the 110] and 1$\text{1}$0] directions, the dislocations being of the edge orientation with Burger's vector equal to $\text{1}\text{2}\text{a<110>}$ and with a different linear density in the two directions. Annealing the system GeTe/SnTe results in a substantial decrease in the density of dislocations due to cross diffusion of Ge and Sn respectively, which forces the dislocations to climb to the surface.