Growth of crystalline γ-Al2O3 on Si by molecular beam epitaxy: Influence of the substrate orientation

This work reports on the molecular beam epitaxy of high quality single crystal γ-Al2O3 thin films on Si(001) and Si(111) substrates. For both substrate orientations, film surfaces are found to be smooth and the oxide-Si interfaces are atomically abrupt without interfacial layers. Reflection high energy electron diffraction, x-ray diffraction, and transmission electronic microscopy characterizations were used to study the epitaxial relationship and the structural quality of the γ-Al2O3 layers depending on the Si substrate orientation. On Si(111), the alumina layers present a high crystalline quality. Evidence is made for a “two-for-three” unit cell indirect epitaxial relationship between γ-Al2O3 and Si(111). On Si(001), after a transition from cubic to hexagonal surface symmetry, the growth planes of γ-Al2O3 change from (001) to (111) leading to a bidomain growth.