BALANCING SURFACE-ENERGY TERMS FOR STABLE GROWTH OF PLANAR SURFACES

We investigate the driving forces that determine the growth mode of he teroepitaxial Ge layers grown from solution on Si substrates with orie ntations (001), (011) and (111) by transmission electron microscopy (T EM) and atomic force microscopy (AFM). Using liquid phase epitaxy, we can study the influences of strain and surface energy terms independen tly on effects due to limited surface diffusion. In (001) and (011) or ientated layers, (111) faceted islands form (Stranski-Krastanov growth ). In contrast, (111) orientated layers grow in a two-dimensional step flow growth mode (Frank-van der Merwe growth). We model these investi gations in terms of energy minimisation considering surface energy red uction by formation of faceted islands and elastic strain energy relax ation by island formation. The strain energy relaxation by island form ation is calculated by the finite element method. According to our con siderations, two-dimensional growth is obtained by selective increase of the free surface energy of the low indices facet planes to a value higher than that of the substrate surface. Formation of faceted island s thus would increase the total surface energy; as a consequence, isla nd formation is suppressed. By choosing the appropriate solvent and te mperature in solution growth, we can provide for thermodynamically sta ble two-dimensional growth.