Three-dimensional lattice rotation in GaAs nanowire growth on hydrogen -silsesquioxane covered GaAs (001) using molecular beam epitaxy

We report on crystallographic behaviors of inclined GaAs nanowires (NWs) self-crystallized on GaAs (001) substrate. The NWs were grown on hydrogen-silsesquioxane (HSQ) covered substrates using molecular beam epitaxy (MBE). Commonly, the epitaxial growth of GaAs < 111 > B (B-polar) NWs is prominently observed on GaAs (001); however, we yielded a remarkable number of epitaxially grown GaAs < 111 > A (A-polar) NWs in addition to the majorly obtained B-polar NWs. Such NW orientations are always accompanied by a typical inclined angle of 35 degrees from (001) plane. NWs with another inclined angle of 74 degrees were additionally observed and attributed to be < 111 >-oriented, not in direct epitaxial relation with the substrate. Such 74 degrees NWs' existence is related to first-order three-dimensional (3D) lattice rotation taking place at the very beginning of the growth. It turns out that spatially 60 degrees lattice rotation around < 111 > directions at GaAs seeds is essentially in charge of A- and B-polar 74 degrees NWs. Transmission electron microscope observations reveal a high density of twinning in the B-polar NWs and twin-free characteristic in the A-polar NWs.