Strain relief: Mainspring of Ge semiconducting nanostructures growth on LaAlO3(0Â 0Â 1)

We report on the initial growth mechanisms of Ge on LaAlO3(0 0 1), a crystalline oxide with a high dielectric constant (high-κ material). Chemical and structural properties were investigated in situ, through X-ray photoelectron spectroscopy and reflection high-energy electron diffraction, and ex situ by using high-resolution transmission electron microscopy. Ge was deposited by molecular beam epitaxy at 600 °C on a c(2 × 2) reconstructed LaAlO3(0 0 1) surface. At this temperature, a Volmer-Weber growth mode is observed due to a lower LaAlO3(0 0 1) surface free energy. It is characterized by the immediate formation of crystalline nano-islands. The Ge islands are relaxed and present an abrupt interface with the substrate. Some of them exhibit a preferential relationship in their heteroepitaxy, where the Ge(0 0 1) planes are parallel to the LaAlO3(0 0 1) ones, but rotated by 45° in the [0 0 1] direction. An additional rotation of 6° with respect to the growth axis is also observed, which compensates partially for the strain produced by the high lattice parameter mismatch (∼5%) between the semiconductor and the oxide.