Fluorescence x-ray standing wave study on (AlAs)(GaAs) superlattices

X-ray standing waves (XSW) were used to investigate the structure of molecu lar beam epitaxy (MBE) grown (AlAs)(3)(GaAs)(7) short-period superlattices (SPSL). The modulation of the Al K, As L, and Ga L x-ray fluorescence induc ed by XSW was measured at the zero-order superlattice (SL) satellite (AlAs) (GaAs)(004,0) and the GaAs(004) substrate Bragg reflection. From the shape of the fluorescence yield modulations and the diffraction pattern, a model of the interfaces is derived by comparing the experimental data with dynami cal calculations of the x-ray wave held distribution and reflectivity. A st raightforward analysis of the fluorescence measurements at the SL satellite shows that in AlAs layers a high crystalline order is established, whereas in GaAs layers a fraction of the Ga and As atoms is not on ideal lattice s ites, but is displaced towards the substrate. The data can be explained by a model in which, at each AlAs/GaAs interface of the GaAs layers, two Ga at om planes are displaced by 0.035 nm and 0.008 nm and one As atom plane by 0 .023 nm. The displacements within the GaAs layers exhibit a mirror symmetry with respect to the centre of each layer.