Investigation of strain relaxation in GaInAs/GaAs superlattices by X-ray diffuse scattering

Two different superlattices (SLs) of Ga0.8In0.2As/GaAs grown by molecular-beam epitaxy on GaAs[001] have been investigated using the measurements on the X-ray diffuse scattering (DS) and X-ray specular reflectivity. The samples differ in the thickness of the GaAs barrier layers being t(b), = 9 nm for sample I and 2 nm for sample 2 separating the active Ga0.8In0.2As layers of t(a) = 16 and 20 nm, respectively. The X-ray wavelength was chosen just above the Ga absorption edge to get a sufficient scattering contrast between both superlattice components. The large difference in lattice parameter of the (Ga0.8In0.2As) and (GaAs) components initiates the relaxation process within samples, which results in two distinguishable states of relaxation, partial for sample S1 and nearly complete for sample S2. The formation of an ordered dislocation network during the relaxation process leads to appearance of microcrystalline domains within multilayers.In contrast to sample SI, the interaction of strain fields across thin barrier layers of sample S2 results in a weak plastic deformation close to the interfaces, displayed as small-height islands. The theoretical simulations of experimental curves were performed in the framework of distorted-wave Born approximation. (C) 1998 Elsevier Science B.V. All rights reserved.