Anisotropic lattice coherency of GaAs nanocrystals deposited on Si(100) surface by molecular beam epitaxy

Abstract

Lattice coherency and morphology of GaAs nanocrystals grown on Si(100) substrate have been studied by transmission electron microscope in order to see growth mechanism of the nanocrystals. GaAs nanocrystals consisting of four {111} facet planes and a rectangular basal plane with four sides along [01 $\overline{1}$] and [011] directions have grown on the Si surface. Either (011) or (0$\overline{1}$1) lattice planes along the minor axis on the rectangular basal plane in the GaAs nanocrystal are completely-coherent with {011} lattice planes in the Si substrate. On the other hand, another (0$\overline{1}$1) or (011) lattice planes along the major axis are partially-coherent with those in the Si substrate. When the lattice planes of the either (011) or (0$\overline{1}$1), which is randomly determined by local atomic structures, become partially-coherent with those in the Si substrate to relax accumulated lattice strain, the growth rate of nanocrystal is remarkably increased along the direction parallel to unstrained (011) or (0$\overline{1}$1) planes which prevents from each area of the strained {011} planes in the nanocrystals increasing. The anisotropic lattice coherency between the GaAs nanocrystals and the Si substrate causes the anisotropic morphology of the GaAs nanocrystals which is elongated the directions parallel to the strained {011} planes.