The fine structure of X‐ray diffuse scattering in the vicinity of high‐angle superlattice Bragg reflections

Triple‐axis X‐ray diffractometry was used to study diffuse scattering from an AlAs/GaAs superlattice grown on an [001]‐oriented GaAs substrate by molecular beam epitaxy. Reciprocal‐space maps were obtained around the 002 reflection from the superlattice and its low‐angle first‐order satellite. The data obtained reveal quasi‐Bragg diffuse‐scattering sheets caused by conformal behavior of interfacial roughness as well as amplification of diffuse scattering when the incoming or outgoing angle is nearly equal to the Bragg angle of the superlattice or substrate. The observed features of diffuse‐scattering fine structure are explained within the framework of the distorted‐wave Born approximation. Nevertheless, this approximation is shown to be incorrect for quantitative analysis of diffuse scattering. In particular, the observed domination in intensity of the incoming Bragg features over the outgoing ones is shown to reflect the decay rate of the coherent X‐ray field through the diffuse‐scattering channel, which is not negligible relative to the coherent diffraction.