Nucleation mechanisms of self-induced GaN nanowires grown on an amorphous interlayer

摘要: The formation mechanisms of GaN nanowires grown on a Si${}_{x}$N${}_{y}$ amorphous interlayer within self-induced approach by molecular beam epitaxy have been investigated combining in situ reflection high-energy electron-diffraction measurements with ex high-resolution transmission electron microscopy imaging. It is found that initially nucleates as spherical cap-shaped islands wetting angle $42\ifmmode\pm\else\textpm\fi{}{7}^{\ifmmode^\circ\else\textdegree\fi{}}$. Subsequently, these coarsen and undergo shape transition toward the nanowire morphology at an experimental critical radius 5 nm. As epitaxial constraint very weak interlayer, equivalent Laplace pressure due to effects surface stress has taken into account. Analytical finite-element method calculations show results nanoscale dimensions significant volume elastic strain both caps nanowires. From thermodynamic considerations, it revealed related energy density slightly favor geometry owing its higher ability relieve strain. Nevertheless, anisotropy even stronger driving force, since are composed $c$- $m$-planes low energies. deduced barrier does exit for may be edge effects, resulting growth condition-dependent radius.