Interface morphology and relaxation in high temperature grown Si1-xCex/Si superlattices

High resolution diffraction is used to investigate the interface morphology and strain relaxation in Si1-xGex/Si superlattices grown at high temperatures. A test structure (ten-period superlattice of 15 nm period length) grown using different deposition rates (0.1-0.4 nm/s), temperatures (420-750 degrees C) and Ge compositions x (0.3-0.46) is examined. Reciprocal space mapping reveals that all these structures, despite their metastability, retain the substrate lattice constant parallel to the surface. However, superlattice features broaden with increasing temperature, growth rate and germanium concentration indicating local variations of the lattice spacing and orientation. Superlattice peaks also exhibit side lobes in reciprocal space, consistent with a lateral undulation of the interfaces. Angle of incidence <(11)over bar 3> rocking scans show that the wavelength of the undulation is of the order of 200 nm and tends to increase with growth temperature and decrease with increasing Ge composition or growth rate.