Pseudomorphic molecular beam epitaxy growth of γ-Al2O3(001) on Si(001) and evidence for spontaneous lattice reorientation during epitaxy

Single crystal γ-Al2O3 thin films have been epitaxially grown by molecular beam epitaxy at 850°C on Si(001) substrates. Reflection high energy electron diffraction and transmission electron microscopy experiments evidence the good crystalline quality of the Al2O3 layer. The present study shows that the two first monolayers of γ-Al2O3 are (001) oriented and coherently strained on Si. For larger thickness, a transition from (001)- to (111)-oriented Al2O3 occurs, together with the apparition of domains in the layer. In-plane epitaxial relationship between Al2O3 and Si(001) are deduced from these observations.