X-RAY-SCATTERING STUDY OF LATTICE-RELAXATION IN ERAS EPITAXIAL LAYERS ON GAAS

We present the results of a high-resolution x-ray scattering study of the lattice relaxation in [001]ErAs epitaxial layers grown on [001]GaAs. Three thickness regimes are found. ErAs is pseudomorphic on GaAs for thicknesses below 70 angstrom and between 70 and 300 angstrom lattice relaxation is observed concomitant with an increase of the in-plane mosaic due to the formation of misfit dislocations. Above 300 angstrom, the out-of-plane transverse scattering from the ErAs lattice planes is no longer specular and further relaxation appears to be related to the out-of-plane mosaic. The ratio of elastic constants, C-12/C-11, is measured to be 0.126. Thin-film interference oscillations are observed and modeled, finding that for 140 angstrom of ErAs the interface fluctuations are approximately 2.5 monolayers. ErAs/GaAs is an ideal system for x-ray scattering studies of lattice relaxation and structure in epitaxial layers.