Time evolution of the microstructures of LaAlO3 thin films grown on Si substrates

The structure and stability of amorphous LaAlO3 thin films deposited on Si substrates were investigated by an X-ray reflectivity technique. The results show that the film/substrate interface contains a LaxAlyOzSi layer and a SiOx layer. X-ray reflectivity profiles showed a continuous change after the films were exposed to ambient air for six months at room temperature. The X-ray reflectivity simulations suggest a diffusion of La and Al (mostly La) from the LaAlO3 layer to the LaxAlyOzSi layer. This process stopped after about six months, and then the films reached a relative equilibrium state. Moreover, post-air-exposure annealing at 300 C in air atmosphere could not change the final distributions of La and Al along the normal to the film's substrate. On the other hand, the leakage-current density slightly decreases after annealing at 300 C, which might be caused by the decrease of oxygen vacancies in the films. (orig.)