Strain relaxation of epitaxial SrTiO3 thin films on LaAlO3 by two-step growth technique

Using pulsed-laser deposition, a two-step growth technique was applied to epitaxial SrTiO3 (STO) thin films on LaAlO3 substrates providing a way to obtain an effective strain relaxation in these films otherwise strained due to lattice mismatch between film and substrate. By changing the thickness of a first layer, deposited at a temperature as low as 100°C before the deposition of the main layer at 750°C, different strain relaxation states of the films could be systematically realized. With a 10-nm-thick first layer, an almost full strain relaxation at the deposition temperature of the main layer was achieved, suggesting a strong impact of this method on strain relaxation. The in-plane dielectric measurements displayed that the ferroelectric transition temperature increases with strain relaxation during the growth. This trend is correct and compatible with the theoretical prediction of the behavior of strained STO derived from Landau theory.