COMBINING 4-CRYSTAL 7-REFLECTION AND 3-CRYSTAL 5-REFLECTION DIFFRACTOMETRY FOR THE CHARACTERIZATION OF ZNSE LAYERS GROWN ON GAAS BY MOVPE

We report on a study on the relaxation, strain and misoriented growth of epitaxial ZnSe layers on (001)-oriented GaAs substrates (2-degrees off) as a function of layer thickness which ranges from 36 nm to 8.5 mum. The thin pseudomorphic layers show clear thickness fringes indicating the good crystalline quality of the samples. For thicker samples, the correlation between misoriented growth of the layer and the relaxation is investigated and compared with calculations of the critical thickness. High-resolution (HR) rocking curves are employed to determine precisely the substrate miscut, the relative crystallographical tilt between substrate and layer, and an additional relative tilt around the face-normal of the sample (phi-axis). Triple-axis (TA) optics are used to record two-dimensional reciprocal space maps around symmetrical Bragg peaks for distinct azimuthal (phi) positions of the sample and maps around asymmetrical Bragg peaks. A strain analysis based on the two-dimensional reciprocal space maps is compared with an analysis based on the rocking-curve method. The additional phi tilt influences the results of both methods. It turns out that the phi tilt depends not only on growth temperature, but also on the sample thickness. Pendellosung fringes are simulated using the dynamical theory of x-ray diffraction.