Interplay of surface morphology, strain relief, and surface stress during surfactant mediated epitaxy of Ge on Si

Lattice-mismatch-induced surface or film stress has significant influence o n the morphology of heteroepitaxial films. This is demonstrated using Sb su rfactant-mediated epitaxy of Ge on Si(lll). The surfactant forces a two-dim ensional growth of a continous Ge film instead of islanding. Two qualitativ ely different growth regimes are observed. Elastic relaxation: Prior to the generation of strain-relieving defects the Ge film grows pseudomorphically with the Si lattice constant and is under strong compressive stress. The G e film relieves strain by forming a rough surface on a nm scale which allow s partial elastic relaxation towards the Ge bulk lattice constant. The unfa vorable increase of surface area is outbalanced by the large decrease of st rain energy. The change of film stress and surface morphology is monitored in situ during deposition at elevated temperature with surface stress-induc ed optical deflection and high-resolution spot profile analysis low-energy electron diffraction. Plastic relaxation: After a critical thickness the ge neration of dislocations is initiated. The rough phase acts as a nucleation center for dislocations. On Si(lll) those misfit dislocations are arranged in a threefold quasi periodic array at the interface that accommodate exac tly the different lattice constants of Ce and Si.