Inclined inheritance of interface roughness in semiconductor superlattices as characterized by x-ray reciprocal space mapping

The inclined inheritance of interface roughness is investigated for an AlAs/GaAs superlattice grown by molecular beam epitaxy on a vicinal (001) GaAs substrate. As a consequence of vertical correlation of the roughness of subsequent interfaces the diffusely scattered x-ray intensity is bunched into resonant diffuse scattering (RDS) sheets in reciprocal space. Inclined inheritance leads to corresponding shearing of the RDS sheets. A simple model for the evaluation of inclined roughness inheritance in three dimensions is presented, where the sheared RDS sheets are modeled by anisotropic sheared ellipsoids. From measurements at different azimuthal sample orientations the two angles characterizing the inclined inheritance of interface roughness can be determined accurately. At the present sample the inheritance of interface roughness approximately follows the direction of step flow during growth. The results show that a three-dimensional analysis of diffuse scattering is necessary for a correct evaluation and interpretation.