Investigation of the growth mechanism and crystallographic structures of GaSb dots nucleation layer and GaSb thin film grown on Si(001) substrate by molecular beam epitaxy

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Abstract
We investigated the growth mechanism and crystallographic structures of GaSb dots as a nucleation layer and GaSb thin films grown on a Si(001) substrate by molecular beam epitaxy using atomic force microscopy and transmission electron microscopy (TEM). The surface morphology of the 100-nm-thick GaSb with GaSb dots drastically changed from that without them. As the GaSb dots gradually grew in size, the coalescence between the adjacent dots was repeated and the space between them was filled, thereby changing the growth mode of GaSb to two-dimensional growth and forming domain structures with terrace surfaces. The high-resolution TEM images and fast Fourier transform patterns revealed that the lattice-mismatched strain in the epitaxial GaSb thin film was almost completely relieved. Because some adatoms were rotated by 60° on the {111} facets and formed a monolayer with a wurtzite structure as a stacking fault in the initial growth stage, twinned GaSb with an inclination of 54.7° from the (001) plane was formed in addition to epitaxial GaSb. The lattice-mismatched strain was nearly relieved in the vicinity of the GaSb/Si interface because of the multiple periodic 90° and 60° misfit dislocation arrays. The formation of GaSb dots, which acted as crystal nuclei and induced periodic misfit dislocation arrays, was useful for the epitaxial growth of GaSb thin films on a Si(001) substrate—a result that will be advantageous for growing high-quality GaSb thin films, with flatter and fewer crystal defects, on a Si(001) substrate in future.

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