Real-time measurement of SrO epilayer strain on H-terminated Si

SrO is a well-known buffer layer on Si for SrTiO3 and BaTiO3 which are highly desirable complex oxides for future generation transistor gate dielectric and ferroelectric memory applications. Furthermore, these complex oxides work as good substrates for various functional oxides including high-Tc superconductors. To fabricate integrated devices of semiconductors and such oxide materials, the epitaxial growth of SrO films on Si is very attractive. However, these properties depend strongly on the quality of thin oxide films in which large mechanical stress might be produced during their preparation. To characterize the film stress as a function of Si surface conditions, we use real-time measurement of substrate curvature during Sr film growth both on bare Si (111) 7x7 and on H-terminated Si(111). The growth of epitaxial Sr films has been achieved at room temperature by MBE. At the beginning of Sr growth on bare Si(111) 7x7, strong compressive stress is generated, indicating an immediate expansion of the surface. The compressive stress in Sr film is a result of strong interfacial strain from lattice mismatch between the film and the substrate. In case of Sr growth on H-terminated Si, however, the maximum total stress in the film is one-third of the film stress on bare Si. Stress-free Sr layers are grown from a thickness of 3 atomic layers corresponding to 1 unite cell. (Authors)