Influence of annealing process and its associated atomic migrations on the Si/LaAlO3(001) nanostructure nucleation

Abstract

We report here on the atomic migration and associated nucleation mechanisms of Si nanocrystals on LaAlO3(001) surface, a high-κ crystalline oxide. Chemical and structural properties were investigated using X-ray photoelectron spectroscopy, X-ray photoelectron diffraction (XPD), reflection high-energy electron diffraction (RHEED), and ex situ with atomic force microscopy. The Si deposition was achieved by molecular beam epitaxy at room temperature. The morphological and chemical properties were followed as a function of isochronal post-growth annealing at increasing temperatures up to 800°C by 100°C steps. Up to 500°C the Si layer remains amorphous without any interdiffusion and interfacial alloy formation. Above 500°C Si nanocrystals nucleate on the surface by transformation of the amorphous Si layer into Si crystalline islands. Two kinds of annealing treatments were performed (direct current and electronic bombardment), leading to a better crystal quality (without stacking faults or twins) for a direct current heating process. Finally, a preferential epitaxial relationship between LaAlO3 and the Si islands was deduced by RHEED and confirmed by XPD: Si(001) planes are parallel to the LaAlO3(001) surface and rotated by 45° around the [001] growth axis.