Improving Epitaxial Growth of γ‐Al2O3 Films via Sc2O3/Y2O3 Oxide Buffers

Heteroepitaxial growth of γ‐Al2O3 on Sc2O3/Y2O3/Si (111) is achieved with oxygen plasma‐assisted molecular beam epitaxy in order to prevent polycrystalline grain boundary formation caused by lattice mismatch. Substrate temperature as well as oxygen flow are adjusted to optimize epitaxial growth conditions around 715–760 °C and 1.9 sccm, respectively. Epitaxial growth is monitored in situ by reflection high‐energy diffraction, while surface morphology is studied by scanning electron microscopy ex‐situ. X‐ray diffraction indicates epitaxial out‐of‐plane 111 orientation with oxygen flow above 0.6 sccm. However, transmission electron microscopy shows stacking fault formation for high oxygen flows. Finally, nanobeam electron diffraction confirms Smrčok model of a spinel‐like γ‐Al2O3 crystal structure. Thick epitaxial γ‐Al2O3 layers are deposited on Sc2O3/Y2O3/Si (111) templates that can be suitable as a buffer layer for the integration of GaN on Si (111) substrate. The diffraction pattern matches the cubic spinel‐like model of γ‐Al2O3 from Smrčok considering a twinned crystal structure. As proof principle, GaN growth on γ‐Al2O3/Sc2O3/Y2O3/Si (111) is finally demonstrated.